Allow for skipping logging of requests that meet some criteria

[briantist]

If you have periodic health checks hitting galactory but you still want to log requests, it can be quite annoying that the log is filled with health check requests, masking actual usages.

For example in an AWS environment with an ALB, the log will be filled with requests from ELB-HealthChecker/2.0 (user agent).

I'm thinking it would be nice to exclude certain UAs from logging, or maybe do it by endpoint (can exclude /health/* for example).