Refactor LabelEdit (#32752)

And fix a regression:
https://github.com/go-gitea/gitea/pull/30053#discussion_r1874405470

Major changes:

* rewrite without jquery
* remove the "delete modal", using "link-action" is good enough
* merge "new modal" and "edit modal"

web_src/css/repo.css

@@ -2061,17 +2061,6 @@ td .commit-summary {
   padding: 1em;
 }
 
-.edit-label.modal .form .column,
-.new-label.modal .form .column {
-  padding-right: 0;
-}
-
-.edit-label.modal .form .buttons,
-.new-label.modal .form .buttons {
-  margin-left: auto;
-  padding-top: 15px;
-}
-
 .stats-table {
   display: table;
   width: 100%;