Correct swagger annotations for enums, status codes, and notification state (#37030)

## ⚠️ 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.

modules/structs/repo_collaborator.go

@@ -5,7 +5,7 @@ package structs
 
 // AddCollaboratorOption options when adding a user as a collaborator of a repository
 type AddCollaboratorOption struct {
-	// enum: read,write,admin
+	// enum: ["read","write","admin"]
 	// Permission level to grant the collaborator
 	Permission *string `json:"permission"`
 }