Expose metrics

[uhthomas]

Kipp currently does not expose any metrics. It would be good to expose:

• Go runtime metrics
• High-level metrics (files uploaded, total size, requests, various others)

Prometheus is the current standard for exposing metrics, but it might be interesting to look at opentelemetry too.

[uhthomas]

This is a little better as of v0.2.0, but there is some ways to go for instrumentation.