telemetry support?

[edisonywh]

Hey there! Are there any plans for telemetry support? https://github.com/beam-telemetry/telemetry

I'd be interested in metrics like how long it takes to checkout a connection, checkout rate etc (there are probably a lot more interesting things that I would want but don't know yet).

Something akin to Ecto's telemetry https://hexdocs.pm/ecto/Ecto.Repo.html#module-telemetry-events

I'd be happy to send in a PR too if needed, just maybe need some pointers into how we want to design this and what kind of metrics to send