WIP: add telemetry

[spencerdcarlson]

[zmstone]

Thanks for the PR.

BTW. I originally wanted a solution without {telemetry, "~> 1.0"} in the dependency (and the brod_use_telemetry to be undefined by default). So to push the responsibility to the wrapping project.

[zmstone]

I have changed the base to dev/telemetry let's start instrumenting the code, preferably increment with small PRs.

[maxno-kivra]

This would be very nice to have. What is needed to get this in?

[akosasante]

:wave:  Also looking to help push this forward, @zmstone , how can I help?

[mikpe]

Use dependency injection. Have measurement points invoke a local, "virtual", telemetry module. That module checks if a telemetry callback module has been registered in the environment: if it has, pass the telemetry on to it, if not, do nothing. The end result is that this project has no hard-coded dependencies in any telemetry framework, but the user can hook one up via the callback module they control.