Add harbor_registry_integration feature flag

app/controllers/groups/harbor/repositories_controller.rb

app/controllers/projects/harbor/application_controller.rb

app/controllers/projects/harbor/repositories_controller.rb

app/views/groups/harbor/repositories/index.html.haml

app/views/projects/harbor/repositories/index.html.haml

...feature_flags/development/harbor_registry_integration.yml

config/routes/group.rb

config/routes/project.rb

ee/spec/features/groups/navbar_spec.rb

ee/spec/features/projects/navbar_spec.rb

lib/sidebars/groups/menus/packages_registries_menu.rb

lib/sidebars/projects/menus/packages_registries_menu.rb

locale/gitlab.pot

spec/features/groups/navbar_spec.rb

spec/features/projects/navbar_spec.rb

...ib/sidebars/groups/menus/packages_registries_menu_spec.rb

.../sidebars/projects/menus/packages_registries_menu_spec.rb

spec/requests/groups/harbor/repositories_controller_spec.rb

.../requests/projects/harbor/repositories_controller_spec.rb

spec/support/helpers/navbar_structure_helper.rb