Merge branch '250699-epic-index' into 'master'

.rubocop_todo/search/namespaced_class.yml

.rubocop_todo/style/redundant_self.yml

config/feature_flags/ops/search_index_curation_epics.yml

ee/app/models/ee/epic.rb

...p/services/elastic/process_initial_bookkeeping_service.rb

ee/app/workers/concerns/elastic/migration_create_index.rb

ee/app/workers/elastic/namespace_update_worker.rb

ee/elastic/migrate/20230518135700_create_epic_index.rb

ee/lib/elastic/latest/epic_class_proxy.rb

ee/lib/elastic/latest/epic_config.rb

ee/lib/elastic/latest/epic_instance_proxy.rb

ee/lib/elastic/v12p1/epic_class_proxy.rb

ee/lib/elastic/v12p1/epic_instance_proxy.rb

ee/lib/gitlab/elastic/helper.rb

ee/lib/tasks/gitlab/elastic.rake

.../elastic/migrate/20230518135700_create_epic_index_spec.rb

ee/spec/elastic/migrate/migration_shared_examples.rb

ee/spec/lib/elastic/latest/epic_config_spec.rb

ee/spec/lib/elastic/latest/epic_instance_proxy_spec.rb

ee/spec/models/epic_spec.rb