Migrate `alert-callout-class-haml-rb` in `ee/app/views/users/available_group_templates.html.haml`

Detected usage of deprecated bs-callout class(es). Most instances of this should use Pajamas::AlertComponent instead, but some may need different treatment (e.g., Pajamas::EmptyStateComponent).

Implementation guide

1. Use Pajamas::AlertComponent to replace .bs-callout in ee/app/views/users/available_group_templates.html.haml
2. Test locally to make sure everything still works correctly.
3. Add before and after screenshots to MR