Behaviour for process context management?

[garthk]

Further to the discussion about :seq_trace we ended up having in absinthe-graphql/absinthe#757, and it being polite to come up with a way to not stuff up people already using the label, it occurs to me we could:

• define a @behaviour for remembering a span context for the current process, retrieving it later, and retrieving it from our parents
• provide one implementation satisfying it with the process dictionary
• provide another satisfying it :seq_trace
• let people configure which one they wanted to use

… and then if someone needed the seq_trace using the seq_trace label already, they could whip up their own implementation to coordinate things.

Such a behaviour should properly be configured and used from :opencensus, but I'll prototype it in Elixir in our app's fork of with_child_span/3 and report back on how it goes.

[tsloughter]

This is what I'm doing with a proposal implementation for OpenTelemetry Erlang lib. I hope to have a PR open in the next day or so for comment.

[garthk]

Moot, given the OT work.