Fix N+1 in the RootController#index

What does this MR do?

This MR adds group: :saml_provider preloading to RootController#index. It only affects EE since SamlProvider is defined in ee/

Bullet output

USE eager loading detected: Group => [:saml_provider] Add to your finder: :includes => [:saml_provider]

  Group => [:saml_provider]
  Add to your finder: :includes => [:saml_provider]
Call stack
  /home/dgruzd/projects/gdk-ee/gitlab/ee/lib/gitlab/auth/group_saml/sso_enforcer.rb:35:in `group_access_restricted?'
  /home/dgruzd/projects/gdk-ee/gitlab/ee/app/policies/ee/project_policy.rb:360:in `block (2 levels) in <module:ProjectPolicy>'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/condition.rb:23:in `instance_eval'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/condition.rb:23:in `compute'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/condition.rb:44:in `block in pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/base.rb:303:in `cache'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/condition.rb:44:in `pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/rule.rb:81:in `pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/rule.rb:211:in `block in pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/rule.rb:211:in `all?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/rule.rb:211:in `pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/step.rb:81:in `pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:101:in `block in run'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:180:in `block in steps_by_score'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:149:in `loop'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:149:in `steps_by_score'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:82:in `run'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:60:in `pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/base.rb:234:in `block in allowed?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/base.rb:234:in `all?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/base.rb:234:in `allowed?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/rule.rb:159:in `pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/step.rb:81:in `pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:92:in `block in run'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:180:in `block in steps_by_score'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:149:in `loop'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:149:in `steps_by_score'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:82:in `run'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/runner.rb:60:in `pass?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/base.rb:234:in `block in allowed?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/base.rb:234:in `all?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/base.rb:234:in `allowed?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/declarative_policy/base.rb:226:in `can?'
  /home/dgruzd/projects/gdk-ee/gitlab/app/models/ability.rb:72:in `allowed?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/allowable.rb:6:in `can?'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/ci/status/pipeline/common.rb:9:in `has_details?'
  /home/dgruzd/projects/gdk-ee/gitlab/app/views/ci/status/_icon.html.haml:4:in `_app_views_ci_status__icon_html_haml___1447165652462024427_69906515539660'
  /home/dgruzd/projects/gdk-ee/gitlab/app/views/shared/projects/_project.html.haml:72:in `block in _app_views_shared_projects__project_html_haml___2025266365514881601_46976728912880'
  /home/dgruzd/projects/gdk-ee/gitlab/app/views/shared/projects/_project.html.haml:21:in `_app_views_shared_projects__project_html_haml___2025266365514881601_46976728912880'
  /home/dgruzd/projects/gdk-ee/gitlab/app/views/shared/projects/_list.html.haml:41:in `block in _app_views_shared_projects__list_html_haml___1613161062491844639_69906517702780'
  /home/dgruzd/projects/gdk-ee/gitlab/app/views/shared/projects/_list.html.haml:39:in `each_with_index'
  /home/dgruzd/projects/gdk-ee/gitlab/app/views/shared/projects/_list.html.haml:39:in `_app_views_shared_projects__list_html_haml___1613161062491844639_69906517702780'
  /home/dgruzd/projects/gdk-ee/gitlab/app/views/dashboard/projects/_projects.html.haml:1:in `_app_views_dashboard_projects__projects_html_haml___467840495428519204_69906519315880'
  /home/dgruzd/projects/gdk-ee/gitlab/app/views/dashboard/projects/index.html.haml:15:in `_app_views_dashboard_projects_index_html_haml___3170368486895918449_69906490868600'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/application_controller.rb:134:in `render'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/dashboard/projects_controller.rb:61:in `block in render_projects'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/gitaly_client.rb:309:in `allow_n_plus_1_calls'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/dashboard/projects_controller.rb:60:in `render_projects'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/dashboard/projects_controller.rb:20:in `block (2 levels) in index'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/dashboard/projects_controller.rb:18:in `index'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/root_controller.rb:25:in `block in index'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/gitaly_client.rb:309:in `allow_n_plus_1_calls'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/root_controller.rb:23:in `index'
  /home/dgruzd/projects/gdk-ee/gitlab/ee/lib/gitlab/ip_address_state.rb:10:in `with'
  /home/dgruzd/projects/gdk-ee/gitlab/ee/app/controllers/ee/application_controller.rb:44:in `set_current_ip_address'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/application_controller.rb:491:in `set_current_admin'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/session.rb:11:in `with_session'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/application_controller.rb:482:in `set_session_storage'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/i18n.rb:55:in `with_locale'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/i18n.rb:61:in `with_user_locale'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/application_controller.rb:476:in `set_locale'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/error_tracking.rb:50:in `with_context'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/application_controller.rb:541:in `sentry_context'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/application_controller.rb:469:in `block in set_current_context'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/application_context.rb:52:in `block in use'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/application_context.rb:52:in `use'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/application_context.rb:20:in `with_context'
  /home/dgruzd/projects/gdk-ee/gitlab/app/controllers/application_controller.rb:462:in `set_current_context'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/metrics/elasticsearch_rack_middleware.rb:24:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/metrics/redis_rack_middleware.rb:22:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/rails_queue_duration.rb:29:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/metrics/rack_middleware.rb:17:in `block in call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/metrics/transaction.rb:54:in `run'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/metrics/rack_middleware.rb:17:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/request_profiler/middleware.rb:17:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/query_limiting/middleware.rb:17:in `block in call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/query_limiting/transaction.rb:39:in `run'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/query_limiting/middleware.rb:16:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/ee/lib/gitlab/database/load_balancing/rack_middleware.rb:39:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/ee/lib/gitlab/jira/middleware.rb:19:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/go.rb:20:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/etag_caching/middleware.rb:13:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/multipart.rb:140:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/read_only/controller.rb:51:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/read_only.rb:18:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/same_site_cookies.rb:27:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/basic_health_check.rb:25:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/handle_ip_spoof_attack_error.rb:25:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/request_context.rb:23:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/config/initializers/fix_local_cache_middleware.rb:9:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/static.rb:11:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/webpack/dev_server_middleware.rb:27:in `perform_request'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/metrics/requests_rack_middleware.rb:60:in `call'
  /home/dgruzd/projects/gdk-ee/gitlab/lib/gitlab/middleware/release_env.rb:12:in `call'

Screenshots

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry
• Documentation (if required)
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• Label as security and @ mention @gitlab-com/gl-security/appsec
• The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• Security reports checked/validated by a reviewer from the AppSec team