test(otlp-trace-metrics): align cross-tracer attributes

[mabdinur]

Summary

• Removes Test_FR07_Otel_Semantics_Mode, its fixture, and related documentation because OTLP trace metrics always emit supported datadog.* attributes.
• Preserves the retired FR07 node IDs as irrelevant manifest tombstones.
• Adds coverage for datadog.svc_src, Boolean datadog.is_trace_root, and datadog.span.top_level values.
• Uses OTLP traces in the service-source test so _dd.svc_src is derived by each tracer rather than injected by the test.
• Enables DD_TRACE_STATS_ADDITIONAL_TAGS using each tracer's experimental-feature configuration and narrows manifest gates to individual unsupported tests.

Implementation PRs:

• Go #5155
• Java #12144
• .NET #8992
• Node.js #9685
• libdatadog #2316

.NET process-tag and peer-tag support remains separate in #9002.

Validation

• Ruff formatting, mypy, yamllint, yamlfmt, and manifest validation
• Collection of all 52 OTLP trace-metrics tests
• Local runs against the Go, Java, .NET, and Node.js implementation branches

[github-actions]

CODEOWNERS have been resolved as:

manifests/cpp.yml                                                       @DataDog/dd-trace-cpp
manifests/dotnet.yml                                                    @DataDog/apm-dotnet @DataDog/asm-dotnet
manifests/golang.yml                                                    @DataDog/dd-trace-go-guild
manifests/java.yml                                                      @DataDog/asm-java @DataDog/apm-java
manifests/nodejs.yml                                                    @DataDog/dd-trace-js
manifests/php.yml                                                       @DataDog/apm-php @DataDog/asm-php
manifests/python.yml                                                    @DataDog/apm-python @DataDog/asm-python
manifests/ruby.yml                                                      @DataDog/ruby-guild @DataDog/asm-ruby
manifests/rust.yml                                                      @DataDog/apm-rust
tests/parametric/test_otlp_trace_metrics.py                             @DataDog/system-tests-core @DataDog/apm-sdk-capabilities

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[zacharycmontoya]

LGTM feature-wise with a couple of comments

[datadog-datadog-prod-us1]

🎉 All green!

🧪 All tests passed
❄️ No new flaky tests detected

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