OpenTelemetry-compatible backends (OTLP)

[stevapple]

Is your feature request related to a problem? Please describe.
OpenTelemetry is a new and widely adopted standard in distributed tracing. Many well-known backends are OTLP-compatible now, so adding OTLP support will unblock new backends as well as improving already-supported backends like Jaeger.

Describe the solution you'd like
Implements OTLP support and add a new OpenTelemetry-compatible backend support.

Describe alternatives you've considered
Don’t add OpenTelemetry support at this time. OTLP heavily uses Protobuf, which may be troublesome.

Additional context
Add any other context or screenshots about the feature request here.

[kespineira]

Hi! Any update on this @Pierre-Lannoy? I see you had put it in the 4.0.0 milestone but nothing was done for that milestone.