Add support in the Go SDK for the Baggage specificaition, as described in Sentry Developer Documentation.

Refer SDK Developer Documention for full details

Based originally on the propagation format for distributed context: Baggage

Should be applied in way that allows compatibility with other Sentry SDKs, ensuring proper distributed tracing functionality and simplifying intercommunications, ingestion, and being a good citizen with other 3rd party implementations working with baggage, via consumption or adding to.

Refer to milestones on other Sentry SDKs as well for further information.