Refactor rename user and rename organization (#24052)

This PR is a refactor at the beginning. And now it did 4 things.
- [x] Move renaming organizaiton and user logics into services layer and
merged as one function
- [x] Support rename a user capitalization only. For example, rename the
user from `Lunny` to `lunny`. We just need to change one table `user`
and others should not be touched.
- [x] Before this PR, some renaming were missed like `agit`
- [x] Fix bug the API reutrned from `http.StatusNoContent` to `http.StatusOK`

models/repo/repo.go

@@ -832,3 +832,11 @@ func FixNullArchivedRepository(ctx context.Context) (int64, error) {
 		IsArchived: false,
 	})
 }
+
+// UpdateRepositoryOwnerName updates the owner name of all repositories owned by the user
+func UpdateRepositoryOwnerName(ctx context.Context, oldUserName, newUserName string) error {
+	if _, err := db.GetEngine(ctx).Exec("UPDATE `repository` SET owner_name=? WHERE owner_name=?", newUserName, oldUserName); err != nil {
+		return fmt.Errorf("change repo owner name: %w", err)
+	}
+	return nil
+}