Add retries back on 503s

[kt474]

Retries on 503s were removed as a part of #2099 because we wanted to make sure a proper error message was shown where there was a maintenance outage. This was not the best approach because we still want to keep these retries for other network outages (Cloudflare).

When there is a maintenance outage we can go through the retry logic first and then show the proper error message at the end.