Support protobuf format in MessageToDict and modify helpers accoridngly

[mtoffl01]

Motivation

Built on #6363 to test otlp export when payloads are sent in protobuf format. The pre-existing logic was only checked against json payloads previously.

Changes

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

• Anything but tests/ or manifests/ is modified ? 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, removed or renamed?
  • Get a review from R&P team

[github-actions]

CODEOWNERS have been resolved as:

tests/otel/test_tracing_otlp.py                                         @DataDog/system-tests-core
utils/interfaces/_open_telemetry.py                                     @DataDog/system-tests-core
utils/proxy/_deserializer.py                                            @DataDog/system-tests-core