Enables .NET OTEL Metrics Tests

[link04]

Motivation

Enabling tests to validate support for OTLP Metrics in both Grpc and Http format for the .NET tracer.

Changes

Added a couple of endpoints needed so the tests could pass and update test to validate for AsInt which .NET uses for long values.

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:

manifests/dotnet.yml                                                    @DataDog/apm-dotnet @DataDog/asm-dotnet
tests/parametric/test_otel_metrics.py                                   @DataDog/system-tests-core @DataDog/apm-sdk-capabilities
utils/build/docker/dotnet/parametric/Endpoints/ApmTestApiOtel.cs        @DataDog/apm-dotnet @DataDog/asm-dotnet @DataDog/system-tests-core