No default selection of destination namespace when importing with GH, BB ad Gitea
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### Problem
When user gets to "choose the projects to import" page the personal namespace is selected by default. We also show personal namespace (under `User`) first in the options and then group under `Groups`. However, we don't want to encourage users to import to personal namespaces, rather the opposite, see https://gitlab.com/gitlab-org/gitlab/-/issues/533992+.
### Proposal
The user should still be able to find their personal namespace, but we should not default to it.
Do not select personal namespace by default - nothing is selected when user arrived to the page.
`User` is still above the `Groups`.
Add a validation in case users try to click **Import** or **Import N repositories** without first selecting the destination namespace - show error to user.
## Update
The [recent MR](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/193193) for this work was [reverted](https://gitlab.com/gitlab-org/gitlab/-/merge_requests/192713) because of errors reported in Sentry from the backend. The MR ostensibly blocks a user from importing a github project before selecting a destination. And yet somehow users are importing and getting to the backend error.
```
ArgumentError
Target namespace is required (ArgumentError)
raise ArgumentError, s_('GithubImport|Target namespace is required') if params[:target_namespace].blank?
^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
```
https://new-sentry.gitlab.net/organizations/gitlab/issues/1602627/?project=3
<details>
<summary>Stacktrace</summary>
> from app/services/import/github_service.rb:139:in `target_namespace_path'
> from app/services/import/github_service.rb:63:in `target_namespace'
> from app/services/import/github_service.rb:131:in `validate_context'
> from ee/import/github_service.rb:16:in `validate_context'
> from app/services/import/github_service.rb:16:in `execute'
> from app/controllers/import/github_controller.rb:75:in `create'
> from action_controller/metal/basic_implicit_render.rb:6:in `send_action'
> from abstract_controller/base.rb:224:in `process_action'
> from action_controller/metal/rendering.rb:165:in `process_action'
> from abstract_controller/callbacks.rb:259:in `block in process_action'
> from active_support/callbacks.rb:121:in `block in run_callbacks'
> from app/controllers/application_controller.rb:493:in `set_current_admin'
> from active_support/callbacks.rb:130:in `block in run_callbacks'
> from lib/gitlab/session.rb:11:in `with_session'
> from app/controllers/application_controller.rb:484:in `set_session_storage'
> from active_support/callbacks.rb:130:in `block in run_callbacks'
> from lib/gitlab/i18n.rb:116:in `with_locale'
> from lib/gitlab/i18n.rb:122:in `with_user_locale'
> from app/controllers/application_controller.rb:475:in `set_locale'
> from active_support/callbacks.rb:130:in `block in run_callbacks'
> from app/controllers/application_controller.rb:464:in `set_current_context'
> from active_support/callbacks.rb:130:in `block in run_callbacks'
> from lib/gitlab/ip_address_state.rb:11:in `with'
> from app/controllers/application_controller.rb:470:in `set_current_ip_address'
> from active_support/callbacks.rb:130:in `block in run_callbacks'
> from marginalia.rb:109:in `record_query_comment'
> from active_support/callbacks.rb:130:in `block in run_callbacks'
> from sentry/rails/controller_transaction.rb:34:in `block in sentry_around_action'
> from sentry/hub.rb:138:in `with_child_span'
> from sentry-ruby.rb:515:in `with_child_span'
> from sentry/rails/controller_transaction.rb:18:in `sentry_around_action'
> from active_support/callbacks.rb:130:in `block in run_callbacks'
> from active_support/callbacks.rb:141:in `run_callbacks'
> from abstract_controller/callbacks.rb:258:in `process_action'
> from action_controller/metal/rescue.rb:25:in `process_action'
> from action_controller/metal/instrumentation.rb:74:in `block in process_action'
> from active_support/notifications.rb:206:in `block in instrument'
> from active_support/notifications/instrumenter.rb:58:in `instrument'
> from active_support/notifications.rb:206:in `instrument'
> from action_controller/metal/instrumentation.rb:73:in `process_action'
> from action_controller/metal/params_wrapper.rb:261:in `process_action'
> from active_record/railties/controller_runtime.rb:32:in `process_action'
> from abstract_controller/base.rb:160:in `process'
> from action_view/rendering.rb:40:in `process'
> from action_controller/metal.rb:227:in `dispatch'
> from action_controller/metal.rb:307:in `block in dispatch'
> from lib/gitlab/middleware/action_controller_static_context.rb:23:in `call'
> from action_controller/metal.rb:307:in `dispatch'
> from action_dispatch/routing/route_set.rb:49:in `dispatch'
> from action_dispatch/routing/route_set.rb:32:in `serve'
> from action_dispatch/journey/router.rb:51:in `block in serve'
> from config/initializers/action_dispatch_journey_router.rb:52:in `block in find_routes'
> from config/initializers/action_dispatch_journey_router.rb:25:in `map!'
> from config/initializers/action_dispatch_journey_router.rb:25:in `find_routes'
> from action_dispatch/journey/router.rb:32:in `serve'
> from action_dispatch/routing/route_set.rb:882:in `call'
> from gitlab/experiment/middleware.rb:19:in `call'
> from omniauth/strategy.rb:202:in `call!'
> from omniauth/strategy.rb:169:in `call'
> from omniauth/strategy.rb:470:in `call_app!'
> from omni_auth/strategies/group_saml.rb:41:in `other_phase'
> from omniauth/strategy.rb:195:in `call!'
> from omniauth/strategy.rb:169:in `call'
> from omniauth/strategy.rb:202:in `call!'
> from omniauth/strategy.rb:169:in `call'
> from omniauth/strategy.rb:202:in `call!'
> from omniauth/strategy.rb:169:in `call'
> from omniauth/strategy.rb:202:in `call!'
> from omniauth/strategy.rb:169:in `call'
> from flipper/middleware/memoizer.rb:72:in `memoized_call'
> from flipper/middleware/memoizer.rb:37:in `call'
> from lib/gitlab/metrics/elasticsearch_rack_middleware.rb:16:in `call'
> from lib/gitlab/middleware/sidekiq_shard_awareness_validation.rb:20:in `block in call'
> from lib/gitlab/sidekiq_sharding/validator.rb:42:in `enabled'
> from lib/gitlab/middleware/sidekiq_shard_awareness_validation.rb:20:in `call'
> from lib/gitlab/middleware/memory_report.rb:13:in `call'
> from lib/gitlab/middleware/speedscope.rb:13:in `call'
> from lib/gitlab/database/load_balancing/rack_middleware.rb:23:in `call'
> from lib/gitlab/middleware/rails_queue_duration.rb:33:in `call'
> from lib/gitlab/etag_caching/middleware.rb:21:in `call'
> from lib/gitlab/metrics/rack_middleware.rb:16:in `block in call'
> from lib/gitlab/metrics/web_transaction.rb:46:in `run'
> from lib/gitlab/metrics/rack_middleware.rb:16:in `call'
> from lib/gitlab/middleware/go.rb:21:in `call'
> from lib/gitlab/middleware/query_analyzer.rb:11:in `block in call'
> from lib/gitlab/database/query_analyzer.rb:83:in `within'
> from lib/gitlab/middleware/query_analyzer.rb:11:in `call'
> from lib/ci/job_token/middleware.rb:11:in `call'
> from batch_loader/middleware.rb:11:in `call'
> from rack/attack.rb:103:in `call'
> from apollo_upload_server/middleware.rb:19:in `call'
> from lib/gitlab/middleware/multipart.rb:173:in `call'
> from rack/attack.rb:127:in `call'
> from warden/manager.rb:36:in `block in call'
> from warden/manager.rb:34:in `catch'
> from warden/manager.rb:34:in `call'
> from rack/cors.rb:102:in `call'
> from rack/tempfile_reaper.rb:15:in `call'
> from rack/etag.rb:27:in `call'
> from rack/conditional_get.rb:40:in `call'
> from rack/head.rb:12:in `call'
> from action_dispatch/http/permissions_policy.rb:36:in `call'
> from action_dispatch/http/content_security_policy.rb:36:in `call'
> from lib/gitlab/middleware/read_only/controller.rb:50:in `call'
> from lib/gitlab/middleware/read_only.rb:18:in `call'
> from lib/gitlab/middleware/unauthenticated_session_expiry.rb:18:in `call'
> from rack/session/abstract/id.rb:266:in `context'
> from rack/session/abstract/id.rb:260:in `call'
> from lib/gitlab/middleware/secure_headers.rb:11:in `call'
> from action_dispatch/middleware/cookies.rb:689:in `call'
> from lib/gitlab/middleware/same_site_cookies.rb:27:in `call'
> from action_dispatch/middleware/callbacks.rb:29:in `block in call'
> from active_support/callbacks.rb:101:in `run_callbacks'
> from action_dispatch/middleware/callbacks.rb:28:in `call'
> from sentry/rails/rescued_exception_interceptor.rb:14:in `call'
> from action_dispatch/middleware/debug_exceptions.rb:29:in `call'
> from lib/gitlab/middleware/path_traversal_check.rb:40:in `call'
> from lib/gitlab/middleware/handle_malformed_strings.rb:21:in `call'
> from sentry/rack/capture_exceptions.rb:30:in `block (2 levels) in call'
> from sentry/hub.rb:299:in `with_session_tracking'
> from sentry-ruby.rb:428:in `with_session_tracking'
> from sentry/rack/capture_exceptions.rb:21:in `block in call'
> from sentry/hub.rb:89:in `with_scope'
> from sentry-ruby.rb:408:in `with_scope'
> from sentry/rack/capture_exceptions.rb:20:in `call'
> from action_dispatch/middleware/show_exceptions.rb:31:in `call'
> from lib/gitlab/middleware/basic_health_check.rb:25:in `call'
> from lograge/rails_ext/rack/logger.rb:15:in `call_app'
> from rails/rack/logger.rb:24:in `block in call'
> from active_support/tagged_logging.rb:139:in `block in tagged'
> from active_support/tagged_logging.rb:39:in `tagged'
> from active_support/tagged_logging.rb:139:in `tagged'
> from active_support/broadcast_logger.rb:241:in `method_missing'
> from rails/rack/logger.rb:24:in `call'
> from action_dispatch/middleware/remote_ip.rb:92:in `call'
> from lib/gitlab/middleware/handle_ip_spoof_attack_error.rb:25:in `call'
> from lib/gitlab/middleware/request_context.rb:15:in `call'
> from lib/gitlab/middleware/webhook_recursion_detection.rb:15:in `call'
> from request_store/middleware.rb:19:in `call'
> from rack/method_override.rb:24:in `call'
> from rack/runtime.rb:22:in `call'
> from rack/timeout/core.rb:154:in `block in call'
> from rack/timeout/support/timeout.rb:19:in `timeout'
> from rack/timeout/core.rb:153:in `call'
> from config/initializers/fix_local_cache_middleware.rb:11:in `call'
> from lib/gitlab/middleware/compressed_json.rb:44:in `call'
> from action_dispatch/middleware/executor.rb:14:in `call'
> from lib/gitlab/middleware/rack_multipart_tempfile_factory.rb:19:in `call'
> from lib/gitlab/metrics/requests_rack_middleware.rb:83:in `call'
> from labkit/middleware/rack.rb:22:in `block in call'
> from labkit/context.rb:35:in `with_context'
> from labkit/middleware/rack.rb:21:in `call'
> from rack/sendfile.rb:110:in `call'
> from action_dispatch/middleware/request_id.rb:28:in `call'
> from lib/gitlab/middleware/sidekiq_web_static.rb:20:in `call'
> from rails/engine.rb:536:in `call'
> from rails/railtie.rb:226:in `public_send'
> from rails/railtie.rb:226:in `method_missing'
> from lib/gitlab/middleware/release_env.rb:12:in `call'
> from rack/urlmap.rb:74:in `block in call'
> from rack/urlmap.rb:58:in `each'
> from rack/urlmap.rb:58:in `call'
> from puma/configuration.rb:279:in `call'
> from puma/request.rb:99:in `block in handle_request'
> from puma/thread_pool.rb:389:in `with_force_shutdown'
> from puma/request.rb:98:in `handle_request'
> from puma/server.rb:468:in `process_client'
> from puma/server.rb:249:in `block in run'
> from puma/thread_pool.rb:166:in `block in spawn_thread'
</details>
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issue