Rename CorrelationContext to Baggage (again)

[yurishkuro]

The W3C WG is leaning towards changing the Correlation-Context header name to baggage (w3c/baggage#17).

What does this mean for OTel?

[dyladan]

This should be closed by #517 no?

[yurishkuro]

I think this is a longer-term question than #517. It is both about the header name and the API concept name. W3C WG members raised concerns with the naming "correlation" as confusing & conflicting with other usages of the word. On the other hand, W3C "baggage" is very much a mechanism for user-supplied data, while OTEP 66 did an about face at the last moment from general purpose k/v bag to a more vague "observability-related correlation labels":

While Correlations can be used to prototype other cross-cutting concerns, this
mechanism is primarily intended to convey values for the OpenTelemetry
observability systems.

For backwards compatibility, OpenTracing Baggage is propagated as Correlations
when using the OpenTracing bridge. New concerns with different criteria should
be modeled separately, using the same underlying context propagation layer as
building blocks.

So this ticket, to me, is about whether OTel is going to support true baggage (which also completely covers observability concerns), or continue drawing a distinction between real baggage an OTel Correlations (in which case it should not be using the w3c "baggage" header).

[jmacd]

I think we should avoid figurative terms like "Baggage". The term itself is loaded with baggage at this point. How about calling this "User Data"?

[mtwo]

While the W3C baggage draft needs to become a formal recommendation, the W3C committee believes that it is now ready for implementation. No additional changes are expected, though it is possible (yet unlikely) that changes will occur as the spec goes through the formal W3C review process.

Myself, @mwear , @dyladan , and @SergeyKanzhelev are on the W3C group.

[tsloughter]

I think the W3C name should be stuck with to avoid confusion. If it is an implementation of W3C Baggage specification then it should be called "baggage".