Pull Mirroring Auth Failures Should Disable Mirroring

gitlab-com/gl-infra/production#2822 (closed) was an error ratio violation due to pull mirroring failing on an endpoint with an expired SSL certificate.

Ideally, these failures are avoided because the application can detect them and automatically disable the pull mirroring so that we stop fetching from an endpoint in a known bad state.

Including backoff retries before disabling to address the failure is likely improve the customer experience.

Cc @msmiley