Add invited group members to search results on assignees widget

What does this MR do?

Previously, on the assignees widget the search was too restrictive and omitted any users that have been granted access to the project using the share-with-group features. The reason for this is by default projectMembers are fetched with a relations parameter equal to [DIRECT, INHERITED] (direct project members and members inherited from ancestor groups). To fix this, in the current MR we also add INVITED_GROUPS to the list of relations that allows us to display invited groups member in the search.

How to check the fix?

1. Create two groups A, B
2. Create a project A/Project
3. Add some users to Group B as regular members (as Developer, or other roles)
4. Via A/Project Members page, invite Group B (as Developer, or other role levels)
5. Create some issues in A/Project
6. Visit A/Project Issue Boards page
7. Select any open issue, and try to assign it to a user belonging to Group B exclusively
8. You should see project B group member in the list when searching for their name

Does this MR meet the acceptance criteria?

Conformity

• 📋 Does this MR need a changelog?
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• Documentation (if required)
• Code review guidelines
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• Style guides
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Availability and Testing

• Review and add/update tests for this feature/bug. Consider all test levels. See the Test Planning Process.
• Tested in all supported browsers
• Informed Infrastructure department of a default or new setting change, if applicable per definition of done

Related to #326301 (closed)