Baggage span processor - key predicate

[MikeGoldsmith]

This issue is to track adding a method of selecting what baggage key entries should be copied.

Feedback in the JS contrib PR was to allow a user-provided predicate function. This puts the responsibility on the user to ensure sensitive baggage keys are not copied while also not prescribing how that is determined.

• Baggage span processor - key predicate opentelemetry-js-contrib#2166

          > What about making the baggage items that are added as spans tags configurable, with the option to provide `*` for all - like here: https://github.com/open-telemetry/opentelemetry-java-instrumentation/blob/355003538a4dcf7ec58b6d9be42086c53238bdac/instrumentation/log4j/log4j-appender-2.17/library/README.md?plain=1#L101
  

We had a similar discussion in the .NET contrib project but thought it was more complicated than just using a set of prefixes so created an issue to continue the discussion. The plain processor that copies all baggage entries (like using * in your example) is likely to be accepted first.

• Baggage activity processor - key predicate opentelemetry-dotnet-contrib#1695
  I'd be happy to open a similar issue for Java contrib too if you feel it would be beneficial. It would be additive to the current state of the processor now too.

Originally posted by @MikeGoldsmith in #1290 (comment)