Update ApproversSelect to use GlSearchBoxByType and remove the jQuery and Select2 dependencies

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With the refactor of the RuleForm it should now be more straightforward to improve upon the underlying ApproversSelect code.

It has been noted that ApproversSelect is making use of jQuery and Select2 with a custom implementation of the input search. It would be better for this to make use of GlSearchBoxByType and remove the dependencies on jQuery, Select2 and the very custom code that goes along with it.

This would be inline with our overall aim of removing jQuery entirely

Implementation plan

frontend 2️⃣

  1. Following a similar pattern to the changes made to ee/app/assets/javascripts/approvals/components/branches_select.vue in !55181 (diffs), replace jQuery and Select2 with GitLab UI components
  2. Update tests to match
Edited by 🤖 GitLab Bot 🤖