Add support for Jaeger propagator

[codeboten]

As per spec, we must provide support for the Jaeger propagation format: https://github.com/open-telemetry/opentelemetry-specification/blob/master/specification/context/api-propagators.md#propagators-distribution

[Rashmi-K-A]

Hey @codeboten, could you elaborate on this a bit? Was wondering if I could pick this up!

[codeboten]

Hi @Rashmi-K-A, this issue is to add a new propagator to handle the Jaeger format specified here. Here's an example of an existing propagator that's already implemented: https://github.com/open-telemetry/opentelemetry-python/blob/master/opentelemetry-sdk/src/opentelemetry/sdk/trace/propagation/b3_format.py

[codeboten]

Let me know if you'd like to take this on and I can assign it to you, thanks!

[Rashmi-K-A]

@codeboten yep, I'll take this one!

[codeboten]

Assigned, thanks!

[Rashmi-K-A]

Hi, @codeboten, the implementation of the extractor function for Jaeger format requires a keys method implemented to extract keys with the prefix 'uberctx-'. I took a look at the spec discussion here and I don't see any other way out. Advice on how to proceed please!

[codeboten]

Hey @Rashmi-K-A, looks like it's probably worth addressing this issue first then: #1084, did you want to tackle that one?

[Rashmi-K-A]

Someone picked it up, I'll wait for that issue to be closed before raising a PR!

[codeboten]

Wow that was quick, sounds good!