Add telemetry events

[chrismccord]

[tsloughter]

Found this when looking to see what telemetry events we had available to hook into for an OpenTelemetry instrumentation library :).

I imagine people will want and greatly benefit from being able to easily include flame executions in distributed traces but there are some issues beyond getting telemetry events added, though that is the first step of course.

I'm going to open an issue to go into the issues and track development of a library in https://github.com/open-telemetry/opentelemetry-erlang-contrib but I wanted to mention it in this repo for visibility, since someone might be interested in working on this.