Consider nicer string description of baggage context

[ktoso]

Current printout just uses the default properties which is BaggageContext(_storage: [:]) which reads a bit meh, since we want to hide that _storage.

Specifically, it looks like this today:

BaggageContext(_storage: [Baggage.AnyBaggageContextKey(keyType: MyModule.MyFunKey, _name: nil): Baggage.BaggageContext.(unknown context at $10773422c).ValueContainer(value: ...)])

That's a lot of noise :)

Perhaps the default rendering should only render the keys?

[slashmo]

Agreed, that's an easy win for usability 👍