Add ability for top-level group owners to ban members from the group

Implements frontend for https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/155

What does this MR do and why?

As part of "Git abuse rate limit" feature, this MR adds the ability for top-level group owners to manually ban group members from the UI.

Previously, banning was only done automatically when group members exceeded the set limit for unique project downloads via UI or git clone.

Screenshots or screen recordings

Screen_Recording_2023-01-20_at_2.58.11_PM

How to set up and validate locally

1. Ensure you are running GDK with an Ultimate license. The following command should log true when run in your terminal if this is set up correctly

   echo "License.feature_available?(:unique_project_download_limit)" | rails c

2. Turn on relevant feature flags:

   echo "Feature.enable(:limit_unique_project_downloads_per_namespace_user)" | rails c

3. Create a top-level group
4. Add another user (non-owner) to the group
5. Go to the group page then navigate to the members page (On the left sidebar, select Group information > Members)
6. Ban the non-owner member that you added to the group
7. Validate that the banned member is no longer displayed in the members table
8. Validate that Banned members tab appears and the banned user is included in the table

MR acceptance checklist

This checklist encourages us to confirm any changes have been analyzed to reduce risks in quality, performance, reliability, security, and maintainability.

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