[nodejs] Rename dd-trace-js main branch

[BridgeAR]

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Motivation

Refs https://github.com/DataDog/dd-trace-js/pull/6551

This should ideally just be approved and I can merge it as soon as I merge the one in dd-trace-js to keep the diverging time window as small as possible.

Changes

Renamed master -> main branch

Workflow

1. ⚠️ Create your PR as draft ⚠️
2. Work on you PR until the CI passes
3. Mark it as ready for review
   • Test logic is modified? -> Get a review from RFC owner.
   • Framework is modified, or non obvious usage of it -> get a review from R&P team

:rocket: Once your PR is reviewed and the CI green, you can merge it!

🛟 #apm-shared-testing 🛟

Reviewer checklist

• [ ] If PR title starts with [<language>], double-check that only <language> is impacted by the change
• [ ] No system-tests internal is modified. Otherwise, I have the approval from R&P team
• [ ] A docker base image is modified?
  • [ ] the relevant build-XXX-image label is present
• [ ] A scenario is added (or removed)?
  • [ ] Get a review from R&P team