[OpenTelemetry] Add gcp otel auth extension

[stankiewicz]

Forks https://github.com/open-telemetry/opentelemetry-java-contrib/blob/main/gcp-auth-extension/src/main/java/io/opentelemetry/

Why it is needed - gcp-auth-extension in otel adds auth to all exporters, once fixed, we will be able to remove this module.

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[stankiewicz]

R: @kennknowles

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Summary of Changes

Hello, I'm Gemini Code Assist¹! I'm currently reviewing this pull request and will post my feedback shortly. In the meantime, here's a summary to help you and other reviewers quickly get up to speed!

This pull request introduces a new extension module for Apache Beam that enables GCP authentication for OpenTelemetry OTLP exporters. By leveraging Google Application Default Credentials (ADC), this extension automatically configures exporters to include the necessary authorization headers when communicating with GCP telemetry endpoints, facilitating seamless integration with Google Cloud monitoring and tracing services.

Highlights

• New Module Addition: Added a new module opentelemetry-gcp-auth-extension to provide GCP authentication support for OTLP exporters.
• Build Configuration: Updated BeamModulePlugin.groovy to include necessary OpenTelemetry dependencies and registered the new module in settings.gradle.kts.
• Authentication Logic: Implemented GcpAuthAutoConfigurationCustomizerProvider to handle ADC retrieval and inject authorization headers into OTLP exporters.

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Code Review

This pull request introduces a new extension module, opentelemetry-gcp-auth-extension, to provide GCP authentication support for OpenTelemetry OTLP exporters in Apache Beam. The review feedback highlights several critical improvements: lazily retrieving Google Application Default Credentials (ADC) to prevent application startup crashes when ADC is not configured and GCP is not targeted; avoiding resource leaks by ensuring the original exporters are shut down when new ones are built; preventing potential NullPointerExceptions during header flattening; and refining endpoint checks to avoid noisy warnings when non-GCP endpoints are used.

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[kennknowles]

Are there classes that can be @Internal if they are not meant for users - since we want to change it.