Batch delete issue and improve tippy opts (#25253)

1. Add "batch delete" button for selected issues, close #22273
2. Address the review in
https://github.com/go-gitea/gitea/pull/25219#discussion_r1229266083

modules/context/base.go

@@ -140,6 +140,10 @@ func (b *Base) JSONRedirect(redirect string) {
 	b.JSON(http.StatusOK, map[string]any{"redirect": redirect})
 }
 
+func (b *Base) JSONOK() {
+	b.JSON(http.StatusOK, map[string]any{"ok": true}) // this is only a dummy response, frontend seldom uses it
+}
+
 func (b *Base) JSONError(msg string) {
 	b.JSON(http.StatusBadRequest, map[string]any{"errorMessage": msg})
 }