Add filter bar to group members view

What does this MR do?

Related to #228675 (closed)

Adds a filtered search bar to the group members view.

There will be a dropdown with sort options added in the next MR. To keep this MR as small as possible it only adds the filtered search bar.

Local testing

Currently behind the group_members_filtered_search feature flag

1. bin/rails console
2. Feature.enable(:group_members_filtered_search)
3. Create a group
4. Add members in "Group" -> "Members"
5. Use the filtered search bar to filter the members

Caveats

• Sort dropdown is not yet implemented, will be in a subsequent MR
• Mixing direct member filter with 2FA filter is not yet supported by the backend, will be fixed in !48084 (merged)

Screenshots (strongly suggested)

View	Before	After
Empty
Search
With filters
Groups tab
Invited tab
Access requests tab

Does this MR meet the acceptance criteria?

Conformity

• [-] Changelog entry
  • Not needed, behind a feature flag
• [-] Documentation (if required)
  • Will be updated before enabling feature flag
• Code review guidelines
• Merge request performance guidelines
• Style guides
• [-] Database guides
• Separation of EE specific content

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

Security

If this MR contains changes to processing or storing of credentials or tokens, authorization and authentication methods and other items described in the security review guidelines:

• [-] Label as security and @ mention @gitlab-com/gl-security/appsec
• [-] The MR includes necessary changes to maintain consistency between UI, API, email, or other methods
• [-] Security reports checked/validated by a reviewer from the AppSec team