W3C Trace Context support

[krystofwoldrich]

Description

• Meta issue Tracing: W3C Trace Context Support team-sdks#41

Tracing headers are implemented in the JS SDK. When JS implements the new headers we have to bump the JS SDK version, add the new options to enable W3C Trace Context headers and update the sample app.

Tasks

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1. Bump JS SDK to version supporting W3C
2. Add option to enable W3C/Sentry headers
3. Verify sentry-trace and trace-parent can be send in parallel
4. Verify incoming trace-parent headers are picked up