Admin Runners Creator Filter Front-End

What does this MR do and why?

Screenshots or screen recordings

This MR aims to allow admins to search by runner creator on the admin runners page.

Part of #378633 (closed)

How to set up and validate locally

1. Create any Runner with a test user from the Admin Runners Page
2. In the search page on the Runners page, choose to filter by Creator, and type or select your user
3. Ensure Step 2 filters the Runners down to those created by the selected user
4. Ensure that typing an invalid/non-existent username results in no Runner results

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.