Support OpenMetrics compatible metrics #14
Description
Is your feature request related to a problem or challenge?
I would like to have access to not only OpenTelementry trace metrics, but also Open Metrics (Prometheus) which are often better suited to long-running trends and aggregate metrics in the observability stack.
Describe the solution you'd like
I would like some interface that provides metrics compatible with the prometheus-client crate so I can integrate them into my application's top level registry and emit the metrics.
Describe alternatives you've considered
As with most software ecosystems, there are always competing packages that accomplish the same end-goal using different approaches. While I have personally chosen the prometheus-client crate for metrics emission, there is the ever popular metrics crate that has more users and needs to be considered as well. It seems important to consider a solution that is compatible with both, even if simply directly supporting the prometheus-client crate would make my life easiest.
I could also see this work being entirely separate from the OpenTememetry/tracing work. While they are absolutely related in many ways, some users may only be set up to, or want to, use one or the other.
Additional context
This was spurred from a discussion here: apache/datafusion#17207