Introduce OStatus::TagManager (#5008)

app/lib/activitypub/activity/create.rb

app/lib/activitypub/tag_manager.rb

app/lib/ostatus/activity/base.rb

app/lib/ostatus/activity/creation.rb

app/lib/ostatus/activity/share.rb

app/lib/ostatus/atom_serializer.rb

app/lib/ostatus/tag_manager.rb

app/lib/tag_manager.rb

app/models/remote_profile.rb

app/serializers/activitypub/delete_serializer.rb

app/serializers/activitypub/note_serializer.rb

app/serializers/rest/status_serializer.rb

app/services/concerns/author_extractor.rb

app/services/fetch_remote_account_service.rb

app/services/fetch_remote_status_service.rb

app/services/process_feed_service.rb

app/services/process_interaction_service.rb

app/services/verify_salmon_service.rb

spec/lib/activitypub/tag_manager_spec.rb

spec/lib/ostatus/atom_serializer_spec.rb