Resolve "Do not fetch all public groups for approval rule when search is empty"

What does this MR do?

This MR updates the groups search for approval rules to only search for all public groups when a search term is present (i.e. all_available=true). Otherwise, when the search term is empty, it will only show groups which the user is a member of (i.e. all_available=false).

Screenshot

(Notice how "cool-public-group" doesn't show up unless it's specifically searched for)

Does this MR meet the acceptance criteria?

Conformity

• Changelog entry Not needed because updated in same release that it was introduced.
• Documentation created/updated or follow-up review issue created
• Code review guidelines
• Merge request performance guidelines
• Style guides
• Database guides
• Separation of EE specific content

Performance and testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.

Links

• Closes #11566 (closed)
• Related #11194 (closed)