Add permission description for API to add repo collaborator (#31744)

Fix #31552.

modules/structs/repo_collaborator.go

@@ -5,6 +5,7 @@ package structs
 
 // AddCollaboratorOption options when adding a user as a collaborator of a repository
 type AddCollaboratorOption struct {
+	// enum: read,write,admin
 	Permission *string `json:"permission"`
 }
 

templates/swagger/v1_json.tmpl

@@ -18484,6 +18484,11 @@
       "properties": {
         "permission": {
           "type": "string",
+          "enum": [
+            "read",
+            "write",
+            "admin"
+          ],
           "x-go-name": "Permission"
         }
       },