Add declarative configuration support

[zeitlinger]

Summary

• Register the distro's resource detector via DeclarativeConfigurationCustomizerProvider (model customizer) and ComponentProvider SPIs for DC mode
• Add InstrumentationDefaults utility for DC-native default configuration — distro authors write defaults.getStructured("micrometer").setDefault("base_time_unit", "s") and the same instance serves both DC mode (model injection) and auto-config mode (otel.instrumentation.* translation)
• ConfigPropertiesBackedConfigProvider (from open-telemetry/opentelemetry-java-instrumentation#15835) bridges ConfigProperties to DC paths automatically

Supersedes #1062.

Candidates for shared utils (otel-java-contrib)

These patterns will be needed by every distro adding DC support:

• InstrumentationDefaults — DC-native API for defining instrumentation defaults, with applyToModel() and toConfigProperties() adapters
• DistroComponentProvider boilerplate — registering a distro resource detector requires walking a null-check chain through ResourceModel → ExperimentalResourceDetectionModel → detectors list; a helper like ModelHelper.ensureResourceDetector(model, name) would simplify this

To be discussed in Java SIG before porting.

Test plan

• ./gradlew :custom:test passes
• InstrumentationDefaultsTest covers toConfigProperties(), applyToModel(), and does-not-override-existing semantics
• Smoke test with DC YAML config once upstream ConfigPropertiesBackedConfigProvider lands

[Copilot]

Pull request overview

Adds support for OpenTelemetry Declarative Configuration (DC) mode in the Grafana Java agent distro by registering the distro resource detector through DC-related SPIs and aligning default instrumentation settings to DC notation.

Changes:

• Register DC model customizer and ComponentProvider implementations via META-INF/services for DC mode.
• Introduce DistroComponentProvider and GrafanaDeclarativeConfigurationCustomizerProvider to ensure the distro resource detector is present in the DC model.
• Express default instrumentation settings in DC notation and translate them into otel.instrumentation.* properties for existing auto-configuration.

Reviewed changes

Copilot reviewed 6 out of 6 changed files in this pull request and generated 1 comment.

Show a summary per file

File	Description
custom/src/main/resources/META-INF/services/io.opentelemetry.sdk.extension.incubator.fileconfig.DeclarativeConfigurationCustomizerProvider	Registers the distro DC model customizer provider via ServiceLoader.
custom/src/main/resources/META-INF/services/io.opentelemetry.sdk.autoconfigure.spi.internal.ComponentProvider	Registers the distro ComponentProvider for DC-based component creation.
custom/src/main/java/com/grafana/extensions/resources/internal/DistroComponentProvider.java	Adds the distro resource detector into the DC model and provides the Resource instance.
custom/src/main/java/com/grafana/extensions/GrafanaDeclarativeConfigurationCustomizerProvider.java	Hooks the model mutation into the DC customization SPI.
custom/src/main/java/com/grafana/extensions/GrafanaAutoConfigCustomizerProvider.java	Moves default instrumentation settings to a DC-defaults map and translates to otel.instrumentation.*.
custom/build.gradle	Adds incubator extension dependency needed for the new DC-related types.

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[zeitlinger]

@jack-berg @jaydeluca @trask I've sketched out how distros can cater both to DC and non-DC.

The key addition (which I'd propose should go to contrib) is this:

class GrafanaDistributionConfig {

  static final InstrumentationDefaults DEFAULTS = new InstrumentationDefaults();

  static {
    DEFAULTS.getStructured("micrometer").setDefault("base_time_unit", "s");
    DEFAULTS.getStructured("log4j_appender").setDefault("experimental_log_attributes", "true");
    DEFAULTS.getStructured("logback_appender").setDefault("experimental_log_attributes", "true");
  }

  private GrafanaDistributionConfig() {}
}

Not sure it it should be static - but the main point is it's similarity to the DC API

[zeitlinger]

Upstream PR open-telemetry/opentelemetry-java-instrumentation#17816 switched InstrumentationDefaults to a nested API:

• setDefault(instr, key, value) → get(instr).setDefault(key, value)
• mirrors DeclarativeConfigProperties.get(name).getString(key) on the read side (note: get is the sugar method added in add "get" method to DeclarativeConfigProperties open-telemetry/opentelemetry-java#7923, not getStructured)

Once #17816 lands, update GrafanaDistributionConfig:

DEFAULTS.getStructured("micrometer").setDefault("base_time_unit", "s");

becomes

DEFAULTS.get("micrometer").setDefault("base_time_unit", "s");