Span.BaggageItem() is Case-Dependent about jaeger-client-go

[yurishkuro]

This is a known limitation of the implementation. We advise users to only use lower-case-snake-case baggage keys.

[tagatac]

Why not fix it here?

[yurishkuro]

preserving the case of the keys requires either a change in the wire format (to store baggage as header values, right now we store the key as part of the header), or an encoding. Either way it will be a breaking change that needs to happen across all client libraries (all languages) and require a lengthy upgrade period until all services are on recent lib versions to make use of the new format. The cost of doing all that work is not worth the convenience of case sensitivity (at least for our team at this time).