## ⚠️ BREAKING ⚠️
- delete reaction endpoints is changed to return 204 No Content rather
than 200 with no content.
## Summary
Add swagger:enum annotations and migrate all enum comments from the
deprecated comma-separated format to JSON arrays. Introduce
NotifySubjectStateType with open/closed/merged values. Fix delete
reaction endpoints to return 204 instead of 200.
When a user has been revoked permission to access a repository, the
related notification could still be visited. But the repository's
information should not be leaked any more.
