Add library_branch tag to Test Optimization reporting

[nccatoni]

Summary

• Tag test results uploaded to Datadog Test Optimization with test.configuration.ci_environment (dev/prod/custom)
• Reuses the existing ci_environment input already computed by compute-workflow-parameters.py
• Updates ci_environment description in system-tests.yml to reflect its usage for Test Optimization tagging

Test plan

• Verify CI runs with dev matrix version produce test.configuration.ci_environment:dev in Test Optimization
• Verify CI runs with prod matrix version produce test.configuration.ci_environment:prod in Test Optimization
• Verify external callers with custom binaries_artifact produce test.configuration.ci_environment:custom

[github-actions]

CODEOWNERS have been resolved as:

.github/actions/push_to_test_optim/action.yml                           @DataDog/system-tests-core
.github/workflows/run-end-to-end.yml                                    @DataDog/system-tests-core
.github/workflows/run-parametric.yml                                    @DataDog/system-tests-core

[cbeauchesne]

Could you use ci_environment which contains dev or prod, it'll make the overall change simpler

[nccatoni]

Do you also want to use ci_environment as the name for the test optimization attribute ?

[cbeauchesne]

Do you also want to use ci_environment as the name for the test optimization attribute ?

yes, it makes sense, WDYT ?

[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

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