OpenTracing being sunset for OpenTelemetry

[NOTE]: # ( ^^ Provide a general summary of the request in the title above. ^^ )

## Summary

I've been reaching out over the past few months to all maintainers of OpenTracing libraries in Erlang or Elixir. I learned about https://github.com/apache/couchdb/tree/prototype/fdb-layer/src/ctrace today and figured I'd do the same even though it is built into couchdb.

[NOTE]: # ( Provide a brief overview of what the new feature is all about. )

## Desired Behaviour

[NOTE]: # ( Tell us how the new feature should work. Be specific. )
[TIP]: # ( Do NOT give us access or passwords to your actual CouchDB! )

Since OpenTracing is being sunset and OpenTelemetry (the merger of OpenTracing and OpenCensus) is its replacement it is likely desirable to users of instrumented libraries that they eventually move to OpenTelemetry, https://opentelemetry.io/

## Possible Solution

[NOTE]: # ( Not required. Suggest how to implement the addition or change. )

There is an official OpenTelemetry Erlang API and SDK (https://github.com/open-telemetry/opentelemetry-erlang-api/ and https://github.com/open-telemetry/opentelemetry-erlang/), along with a SIG to discus implementation. Before today the SIG was only meeting once a month as part of the Erlang Ecosystem Foundation's Observability Working Group, but it will be being updated to meet weekly.

It is certainly not urgent or a must even if OpenTracing the spec is being deprecated, your tracing lib and reporting to Jaeger will continue to work for the foreseeable future -- and I see you have special couchdb specific functionality builtin, so not like you could simply drop in a new lib anyway. I just wanted to reach out like I have to all the others in hopes of collaboration on the future standard of open distributed tracing, metrics and logging in Erlang/Elixir.

Start by reviewing the existing tracing implementation at prototype/fdb-layer/src/ctrace and the linked OpenTelemetry Erlang API and SDK projects. The issue does not name a concrete change, target files, tests, or acceptance criteria, so the desired end state would need to be defined before implementation.

Written by the indexing model from the issue text.