Migrate groups' template setting away from select2

What does this MR do and why?

This migrates the groups' Template setting away from select2. We are replacing it with the ProjectSelect component that we are creating here as well. That new component is based of the EntitySelect component and follows the same patterns as GroupSelect.

Screenshots or screen recordings

Before	After

How to set up and validate locally

1. Navigate to group's Templates setting at :group > Settings > General > Templates.

MR acceptance checklist

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• I have evaluated the MR acceptance checklist for this MR.

Re #374098 (closed)