Baggage span processor - key transformation function

[MikeGoldsmith]

Consider allowing a user provided transformation function that can alter the baggage entry key before adding to span attribute.

          This implementation currently uses the `BaggageEntry` key to be the attribute name. While it can be useful for some users, I guess prefixing it with something like `baggage.{key}` or suggesting some rename capability, can offer enhanced usability and flexibility to end users in the context of a trace.

I was thinking about the possibility to extend this component with a config object that can be used to supply either a spanAttribtePrefix or a spanAttributeName(baggageKey: string): string function to apply more advanced renames. Adding a config object is something we can always address in a future PR without breaking change I think.

Originally posted by @blumamir in #2114 (comment)

[MikeGoldsmith]

Closing as duplicate of #2166