Abuse reports list empty state

What does this MR do and why?

This MR implements Display empty state when there are no reports to show as part of https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/157+.

It updates the abuse reports list to render <GlEmptyState /> component when there are no reports to display.

Screenshots or screen recordings

Screen_Recording_2023-03-14_at_9.19.35_PM

How to set up and validate locally

1. Enable the feature flag

   $ rails console
   > Feature.enable(:abuse_reports_list)

2. Login with an admin account

3. Go to the Abuse Reports page (http://localhost:3000/admin/abuse_reports)

4. Filter reports by a user with associated abuse report

5. Validate that an empty state is shown

   🖼

   

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.