RUM-1555 Update default tracing headers to datadog + W3C (tracecontext)

[maciejburda]

What and why?

Adds W3C tracecontext to default configuration along with datadog headers.

Review checklist

• Feature or bugfix MUST have appropriate tests (unit, integration)
• Make sure each commit and the PR mention the Issue number or JIRA reference
• Add CHANGELOG entry for user facing changes

Custom CI job configuration (optional)

• Run unit tests for Core, RUM, Trace, Logs, CR and WVT
• Run unit tests for Session Replay
• Run integration tests
• Run smoke tests
• Run tests for tools/

[maciejburda]

@ganeshnj Do you think we should quite in the CHANGELOG.md?

[datadog-datadog-prod-us1]

Datadog Report

Branch report: maciey/RUM-1555-default-tracing-update
Commit report: 65f7ac1

✅ dd-sdk-ios: 0 Failed, 0 New Flaky, 2652 Passed, 0 Skipped, 10m 49.78s Wall Time

[ganeshnj]

@ganeshnj Do you think we should quite in the CHANGELOG.md?

Yes we should. Let's keep it consistent across the board.

https://github.com/DataDog/dd-sdk-flutter/pull/501/files

• Change default tracing headers for first party hosts to use both Datadog headers and W3C tracecontext headers.

[ncreated]

Looks good 👌. However, we change default behaviour, so we must update public API comments with new configuration. The change we introduce here impacts these two APIs:

• https://github.com/DataDog/dd-sdk-ios/blob/develop/DatadogTrace/Sources/TraceConfiguration.swift#L100
• https://github.com/DataDog/dd-sdk-ios/blob/develop/DatadogRUM/Sources/RUMConfiguration.swift#L268

[ncreated]

🚀