admin: lower log level to Debug for /metrics requests

[hairyhenderson]

When monitoring Caddy with Prometheus pointed at the default endpoint (http://localhost:2019/metrics), things can get a little verbose:

2020/09/24 00:17:00.484 INFO    admin.api       received request        {"method": "GET", "host": "localhost:2019", "uri": "/metrics", "remote_addr": "127.0.0.1:52404", "headers": {"Accept":["application/openmetrics-text; version=0.0.1,text/plain;version=0.0.4;q=0.5,*/*;q=0.1"],"Accept-Encoding":["gzip"],"User-Agent":["Prometheus/2.21.0"],"X-Prometheus-Scrape-Timeout-Seconds":["10.000000"]}}
2020/09/24 00:17:15.485 INFO    admin.api       received request        {"method": "GET", "host": "localhost:2019", "uri": "/metrics", "remote_addr": "127.0.0.1:52404", "headers": {"Accept":["application/openmetrics-text; version=0.0.1,text/plain;version=0.0.4;q=0.5,*/*;q=0.1"],"Accept-Encoding":["gzip"],"User-Agent":["Prometheus/2.21.0"],"X-Prometheus-Scrape-Timeout-Seconds":["10.000000"]}}
2020/09/24 00:17:30.483 INFO    admin.api       received request        {"method": "GET", "host": "localhost:2019", "uri": "/metrics", "remote_addr": "127.0.0.1:52404", "headers": {"Accept":["application/openmetrics-text; version=0.0.1,text/plain;version=0.0.4;q=0.5,*/*;q=0.1"],"Accept-Encoding":["gzip"],"User-Agent":["Prometheus/2.21.0"],"X-Prometheus-Scrape-Timeout-Seconds":["10.000000"]}}
[... ad nauseum ...]

I'm not ecstatic about this solution, but I feel like it's good enough until we can figure out a better approach. Ideally an admin module would be able to control its own logging in some way. This'll at least make monitoring Caddy with Prometheus a less noisy activity for the 2.2 release...

Signed-off-by: Dave Henderson dhenderson@gmail.com

[mholt]

Thanks for helping to improve things, Dave!

[mholt]

LGTM, thanks!