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_file.go

@@ -72,7 +72,7 @@ type ChangeFileOperation struct {
 	// indicates what to do with the file: "create" for creating a new file, "update" for updating an existing file,
 	// "upload" for creating or updating a file, "rename" for renaming a file, and "delete" for deleting an existing file.
 	// required: true
-	// enum: create,update,upload,rename,delete
+	// enum: ["create","update","upload","rename","delete"]
 	Operation string `json:"operation" binding:"Required"`
 	// path to the existing or new file
 	// required: true