Repair admin tag runner sorting with relative url mounts

What does this MR do and why?

Bugfixes tag sorting on runners in admin area when gitlab is installed with a relative url.

Before, tag sorting failed because the url https:localhost/admin/runners/tag_list.json was searched for when the real path was https:localhost/gitlab/admin/runners/tag_list.json. This change includes the relative url install location to the searched path.

Screenshots or screen recordings

Screenshots are required for UI changes, and strongly recommended for all other merge requests.

Before	After
Recording_2023-07-10_110624	Recording_2023-07-10_105650

How to set up and validate locally

Follow the instructions here.

Navigate to the Admin Area > Ci > Runners

Set up a few runners with <some_tag>

In the search bar, type tags=some_tag

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.