Proposal: Add Jaeger propagator

[TommyCpp]

As detailed in spec, SDK should come with B3 and Jaeger propagators. We already have B3 propagator, so it make sense to add a jaeger propagator.

I'd like to work on that if that sounds good.

[hairyhenderson]

FWIW, I'm in favour of this - we've been working on migrating from OT/Jaeger to OTel internally and trace propagation between services has been a big concern.

Glad to see that open-telemetry/opentelemetry-specification#770 was merged, and I wish that I'd seen that before starting to move some of our services that don't support OTel over to Zipkin (notably, nginx)

[MrAlias]

@TommyCpp thanks for identifying this and picking up the task. The help is definitely appreciated.

We have interpreted the specification ...

MUST be distributed as OpenTelemetry extension packages

as saying the B3 and Jaeger propagators should live in the contrib repository. I'm going to migrate this issue there to track this work.