chore(otel/logs): decouple creating logger from generating log messages

[mabdinur]

Motivation

Decouple logger creation from log message generation to improve API clarity and flexibility.

Changes

• Remove create_logger parameter from write_log API
• Update write_log signature: logger_name, level, message (with optional span_id)
• Add create_logger endpoint tests
• Update all tests to call create_logger explicitly before write_log
• Rename logger names in tests to match test function names

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/parametric/test_otel_logs.py                                      @DataDog/system-tests-core @DataDog/apm-sdk-capabilities
tests/parametric/test_parametric_endpoints.py                           @DataDog/system-tests-core @DataDog/apm-sdk-capabilities
utils/build/docker/nodejs/parametric/server.js                          @DataDog/dd-trace-js @DataDog/system-tests-core
utils/build/docker/python/parametric/apm_test_client/server.py          @DataDog/apm-python @DataDog/asm-python @DataDog/system-tests-core
utils/docker_fixtures/_test_clients/_test_client_parametric.py          @DataDog/system-tests-core