Supporting B3 baggage propagation

[jagdishkulkarni]

Is your feature request related to a problem? Please describe.
Adding support for Jaeger B3 baggage header propagation. Open Telemetry does not support baggage header propagation in a format expected by Jaeger Open tracing. Open Telemetry Java Issue-3661 and Open Telemetry Specification Issue-1971 have been raised for this. As per comments of maintainers this can be added in opentelemetry-java-contrib.

Describe the solution you'd like
Add new Baggage propagator B3BaggagePropagator to make it backward compatible. This will be based on baggage header format mentioned in Jaeger B3TextMapCodec.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

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

[yurishkuro]

Copying from open-telemetry/opentelemetry-specification#1971 (comment)

It was added to Jaeger (jaegertracing/jaeger#755 (comment)), apparently because Brave/Sleuth already used baggage-*** format, although their authors were not especially happy with it (openzipkin/b3-propagation#22 (comment)).

Looking at [Brave docs][1], it does not seem that baggage-*** format is actually standardized in any kind of spec, it's just the examples they used, i.e. they could've used any other naming.