## Summary
Add metrics for the global cache. Configure `otel` to export metrics to
prometheus.
## Related issues
-
[ENG-2407](https://linear.app/pomerium/issue/ENG-2407/add-additional-metrics-and-tracing-spans-to-pomerium)
## Checklist
- [x] reference any related issues
- [ ] updated unit tests
- [ ] add appropriate label (`enhancement`, `bug`, `breaking`,
`dependencies`, `ci`)
- [x] ready for review
