Improved ref switcher dropdown performance

What does this MR do?

Removes jQuery creating elements, instead uses vanilla JS to create elements. This increase the performance significantly, previously with ~500 branches render time was approx. 30ms, with this change it dropped down to approx. 5ms.

The JSON now returns a maximum of 100 branches & 100 tags. The user can then search for more if they require.

What are the relevant issue numbers?

Closes #18202 (closed)

app/assets/javascripts/protected_branches/protected_branch_dropdown.js.es6

@@ -48,7 +48,7 @@ class ProtectedBranchDropdown {
   onClickCreateWildcard() {
     // Refresh the dropdown's data, which ends up calling `getProtectedBranches`
     this.$dropdown.data('glDropdown').remote.execute();
-    this.$dropdown.data('glDropdown').selectRowAtIndex(0);
+    this.$dropdown.data('glDropdown').selectRowAtIndex(gon.open_branches.length);
   }
 
   getProtectedBranches(term, callback) {