Dynamic Sampling baggage header changes

[marandaneto]

• Java/Android Add sample rate to baggage as well as trace in envelope header and flatten user sentry-java#2135 and Feat/traces sampler into sample rate sentry-java#2141 and Only send userid in Dynamic Sampling Context if sendDefaultPii is true sentry-java#2147
• Cocoa - still pending feat: Add transaction to baggage and trace headers sentry-cocoa#1992
• React-Native
• Test Android with a backend integration such as Python
• Test iOS with a backend integration such as Python
• Test RN with a backend integration such as Python - requires Cocoa and Android because of Native SDKs ser/deser.

Sentry Spec https://develop.sentry.dev/sdk/performance/dynamic-sampling-context/
JS implementation: getsentry/sentry-javascript#5292 (there are more PRs related to this)
W3 Spec https://www.w3.org/TR/baggage/

[adinauer]

• Add sample_rate to trace envelope header (should be tracesSampleRate or tracesSampler callback result; see Add tracesSampler as source for sample_rate develop#619)
• Add sentry-sample_rate to baggage (same value as above)
• Rename keys in baggage to have _, e.g. sentry-trace_id instead of sentry-traceid
• Flatten user in trace envelope header into user_id and user_segment

[marandaneto]

@antonpirker please let us know when the backend sample is ready for testing so we can validate on our end as well, thank you for doing this.

[marandaneto]

@brustolin and @adinauer Please consider adding the getsentry/develop#625 check.

[marandaneto]

Consider:

For all implementors of the sampling context: please double check that your implementation always writes the sample rate as a string with only basic floating point numbers (e.g. 0.123). Ensure that whichever stringify function you use never goes into exponent notation for extra small sample rates and you do not serialize invalid values like NaN or Inf (which shouldn't exist in your impl anyway).

[marandaneto]

For now, because of PII reasons, we're ditching the sentry-transaction from the Baggage header.
Also sentry-user_id which was guarded by isSendDefaultPii as well.
Spec is in the making by the Web team.

Edit: See getsentry/develop#635

[marandaneto]

#30 has to be done, but not now for Mobile.

[marandaneto]

#30 is also a mandatory field for DS.
Doc changes https://github.com/getsentry/develop/pull/651/files

[marandaneto]

@brustolin and @adinauer can you tick the boxes in the PR description that are done? Most likely Cocoa, and Test Android/Cocoa?

[adinauer]

To figure out priority of #39 we should check with other teams / SDKs if this was already implemented.