Observability in the Buildkite agent via Datadog

The latest release of Buildkite Agent (version 3.27.0) includes an integration with Datadog APM, providing insights into CI/CD processes. This feature allows users to identify areas for optimization and common errors in their pipelines. The integration was initially submitted by GitHub users goodspark and samschlegel and tested on Buildkite's own CI infrastructure. The tracing data is useful for diagnosing specific CI/CD issues, improving efficiency, and optimizing compute resources. Future plans include supporting other tracing backends and migrating the existing APM implementation to OpenTelemetry.