Allow Runners to discover Job Router endpoint

I'm testing the code in Job Router (gitlab-runner!5945) and getting an error:

ERROR: Getting GitLab instance metadata... failed   correlation_id=01KAZFQQ05FW4X2N79NMF2KS3P runner=6I_uW4-Kh status=GET https://gdk.test:3443/api/v4/metadata: 401 Unauthorized

Unauthenticated users cannot access the /api/v4/metadata endpoint and apparently runners cannot either. We need that access to get kas' URL from the endpoint.