Use metrics crate to publish object store metrics

[wjones127]

Use the metrics crate, which can connect to others like prometheus and otel collectors.

Success criteria:

1. Have all requests with counts, bytes, latency, and error count measured, across labels:
   • Operation (PUT / LIST / HEAD / GET / DELETE)
   • Object store scheme prefix (e.g. azure, s3, gcs)
2. Have a metric for retry and throttle counts, separate by reason (429 vs 503) (this is a stretch goal)
3. metrics is an optional dependency.