Add latest changes from gitlab-org/gitlab@master

lib/gitlab/import_export.rb

lib/gitlab/import_export/importer.rb

lib/gitlab/import_export/snippet_repo_restorer.rb

lib/gitlab/import_export/snippet_repo_saver.rb

lib/gitlab/import_export/snippets_repo_restorer.rb

lib/gitlab/import_export/snippets_repo_saver.rb

scripts/review_apps/automated_cleanup.rb

spec/factories/snippets.rb

...ration/user_mentions/create_resource_user_mention_spec.rb

spec/lib/gitlab/import_export/import_export_spec.rb

spec/lib/gitlab/import_export/importer_spec.rb

spec/lib/gitlab/import_export/snippet_repo_restorer_spec.rb

spec/lib/gitlab/import_export/snippet_repo_saver_spec.rb

spec/lib/gitlab/import_export/snippets_repo_restorer_spec.rb

spec/lib/gitlab/import_export/snippets_repo_saver_spec.rb

spec/migrations/cleanup_empty_snippet_user_mentions_spec.rb

spec/migrations/migrate_snippet_mentions_to_db_spec.rb

spec/migrations/migrate_snippet_notes_mentions_to_db_spec.rb

spec/models/snippet_repository_spec.rb

spec/services/projects/import_export/export_service_spec.rb