Metrics / logging

[willscott]

there is not yet logging.

the pool should track latency and bandwidth of requests as metrics.
logs should be emitted for each successful & failed request

[lidel]

FYSA started mapping things we want to measure in bifrost-gateway, Saturn things are (2) and details TBD.

Some things need to be backend-independent, but we do want Saturn-specific metrics dded to that list and tracked/registered if caboose provides them 👍

[willscott]

#7 should now capture the 3 metrics specified in (2).

let me know if the exposed CabooseMetrics prometheus.Registry is a reasonable interface for the package, or if it's easier for the metrics to be registered against the implicit global registry.

[willscott]

(it was #8 that captured the 3 metrics specified)

fixed with #8