decl. config. enable experimental runtime metrics

[SylvainJuge]

Part of #1054

Equivalent to add the following to declarative configuration

instrumentation/development:
  java:
    runtime_telemetry:
      emit_experimental_metrics/development: true

Users can opt-out by setting it to false which will revert to the upstream default behavior with:

instrumentation/development:
  java:
    runtime_telemetry:
      emit_experimental_metrics/development: false

[coderabbitai]

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📥 Commits

Reviewing files that changed from the base of the PR and between bf2a1ed and 13fba42.

📒 Files selected for processing (2)

• custom/src/main/java/co/elastic/otel/declarativeconfig/ElasticDeclarativeConfigurationCustomizer.java
• custom/src/test/java/co/elastic/otel/declarativeconfig/ElasticDeclarativeConfigurationCustomizerTest.java

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📝 Walkthrough

Walkthrough

Extended ElasticDeclarativeConfigurationCustomizer to configure experimental runtime telemetry metrics. Added a new customization step that ensures the presence of instrumentationDevelopment, java, and runtime_telemetry blocks within the OpenTelemetry configuration model. The implementation sets the emit_experimental_metrics/development property to true by default only when absent. Updated tests verify the new behavior in default configurations and when explicitly set to false.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests

• 🛠️ Update Documentation: Commit on current branch
• 🛠️ Update Documentation: Create PR

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