Separate the features for the B3 Multi and B3 Single propagator support

[zacharycmontoya]

Motivation

OpenTelemetry lists the b3 and b3multi propagators as separate propagators (see their environment variable specification), so we should create separate features to track our support.

Changes

Updates the tests in tests/parametric/test_headers_b3multi.py to use the new b3multi_headers_propagation feature, instead of the b3_headers_propagation.

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

🚀 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

[github-actions]

CODEOWNERS have been resolved as:

tests/parametric/test_headers_b3multi.py                                @DataDog/system-tests-core @DataDog/apm-sdk-capabilities
utils/_features.py                                                      @DataDog/system-tests-core