Baggage doc should be modified to make it less tied to tracing singnal

[cijothomas]

What needs to be changed?

Baggage doc is tied too much to tracing. We need to modify it making it clear that Baggage is applicable across all signals, and potentially show examples on Baggage can be used across signals.

What is the name + path of the page that needs changed?
https://github.com/open-telemetry/opentelemetry.io/blob/main/content/en/docs/concepts/signals/baggage.md

Additional context: Noticed in #3657 (comment).

[svrnm]

Thanks for raising this, I agree, this page needs some attention

[theletterf]

Thanks for raising this. We had a similar conversation on this @flands and I.

[cijothomas]

#1878 Old issue talking about this.

Couple of statements from the same doc that feels incorrect/misleading:

1. However, spans in OpenTelemetry are immutable once created
2. attach information from your application to a span and retrieve that information much later - There is no "read" API to read from span, as per https://opentelemetry.io/docs/specs/otel/trace/api/#span which says "Spans are not meant to be used to propagate information within a process. To prevent misuse, implementations SHOULD NOT provide access to a Span’s attributes besides its SpanContext."

[svrnm]

Yeah, the baggage doc needs some attention...