add process tags to runtime metrics

[wantsui]

What does this PR do?

The purpose is to add process tags to the runtime metrics when enabled.

Motivation:

Follows the Python implementation:

• chore(runtime_metrics): process tags was not a list dd-trace-py#15580
• chore(runtime_metrics): add process_tags dd-trace-py#15465

Addresses AIDM-263
Change log entry

Yes. Add process tags to runtime metrics when DD_EXPERIMENTAL_PROPAGATE_PROCESS_TAGS_ENABLED is enabled.

Additional Notes:

How to test the change?

Locally:

bundle exec rspec spec/datadog/core/runtime/metrics_spec.rb
bundle exec rspec spec/datadog/core/configuration/components_spec.rb
bundle exec rspec spec/datadog/core/environment/process_spec.rb

I updated one of the Rails tests locally to send the metrics, and I can see them correctly get attached when things are enabled:

[marcotc]

Looks good!

[pr-commenter]

Benchmarks

Benchmark execution time: 2026-01-08 20:11:20

Comparing candidate commit 82ff245 in PR branch add-process-tags-to-runtime-metrics with baseline commit 5ec9115 in branch master.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 43 metrics, 2 unstable metrics.

scenario:profiling - stack collector (ruby frames - native filenames enabled)

• 🟩 throughput [+161.060op/s; +162.902op/s] or [+5.210%; +5.270%]

[datadog-official]

✅ Tests

🎉 All green!

❄️ No new flaky tests detected
🧪 All tests passed

🎯 Code Coverage
• Patch Coverage: 100.00%
• Overall Coverage: 95.21% (-0.00%)

View detailed report

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