[ryanmilne-digicert]

This pull request adds comprehensive OpenTelemetry (OTel) metrics and tracing support to the AWS binary, closely aligning it with the POSIX binary's observability features. It introduces a new initialization routine for OTel, exposes configuration options via environment variables and flags, and includes robust documentation and tests for various exporter scenarios.

Key changes include:

OpenTelemetry Integration:

• Added a new initOTel function in otel.go to set up OTel metrics, tracing, and Go runtime metrics using environment-driven exporters (OTLP, Prometheus, or none). This function configures resource attributes, sets up batchers, and ensures proper shutdown on service termination. (cmd/tesseract/aws/otel.go)
• Introduced a --trace_fraction flag to control the sampling rate of root traces, with special handling for periodic Tessera root spans. (cmd/tesseract/aws/main.go)

Configuration and Documentation:

• Updated the AWS binary documentation to explain OTel configuration, including exporter selection, resource attributes, Prometheus endpoint setup, and security considerations. (cmd/tesseract/aws/README.md)

Code Integration:

• Integrated the OTel initialization and shutdown into the main binary startup sequence, ensuring metrics and tracing are active for the service lifetime. (cmd/tesseract/aws/main.go)

Testing:

• Added comprehensive tests for OTel initialization covering Prometheus, OTLP, exporter misconfiguration, port conflicts, and trace sampling. The tests verify correct metrics exposure, resource labeling, and graceful shutdown. (cmd/tesseract/aws/otel_test.go)

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[ryanmilne-digicert]

Meant to create pull request in fork.