Include the registry in the request log

[davidhao3300]

Describe the problem to be solved

Hello! Thank you for this great project. We'd like to track the cache misses by registry/repo in Datadog. We're able to get most of the way by using log-based monitoring using the log line logged here. The main issue is that while we can parse the repository from the path field, we cannot figure out the registry since the "ns" URL param is not logged.

Proposed solution to the problem

The ideal solution would be to parse the ns URL param and put a "registry" field in the log line, but I'm not sure if this is something that work for everyone. Perhaps putting an allow-listed set of URL params instead would be more-generic?