Default to showing open reports when given status filter is invalid

Part of https://gitlab.com/gitlab-org/modelops/anti-abuse/team-tasks/-/issues/157

What does this MR do and why?

Fallback to displaying status = open abuse reports when the specified status filter value is invalid.

Screenshots or screen recordings

Screen_Recording_2023-03-15_at_2.00.19_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. Validate that the list reverts back to filtering displayed reports by Status = Open when given status query value is invalid

5. Validate that the list can be filtered by other valid statuses (closed)

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.