Add more Datadog / OpenTelemetry Baggage API weblog tests

[zacharycmontoya]

Motivation

We need additional tests to assert a standardized Datadog SDK behavior when the in-app user uses both the Datadog Baggage API and OpenTelemetry Baggage API to insert baggage items with conflicting keys

Changes

Adds a new test case tests/test_baggage.py::Test_Baggage_Headers_Api_Combined and its corresponding weblog endpoint /otel_drop_in_baggage_api_combined

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:

docs/weblog/end-to-end_weblog.md                                        @DataDog/system-tests-core
manifests/dotnet.yml                                                    @DataDog/apm-dotnet @DataDog/asm-dotnet
tests/test_baggage.py                                                   @DataDog/system-tests-core
utils/build/docker/dotnet/weblog/Endpoints/OtelDropInEndpoint.cs        @DataDog/apm-dotnet @DataDog/asm-dotnet @DataDog/system-tests-core