Baggage activity processor - key predicate

[MikeGoldsmith]

          I'd prefer if we had a constructor that allowed the user to add a prefix for baggage items that they'd like to add as attributes. We've had situations where customers have used a similar approach and managed to receive data from externally propagated baggage (accidentally).

A pattern like adding a prefix would mean that it becomes a lot more intentional, and therefore just a little safer.

Originally posted by @martinjt in #1659 (comment)

[MikeGoldsmith]

Another suggestion from the JS contrib project is 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