feat(otel): add support for otel metrics

[mabdinur]

What does this PR do?

Adds OpenTelemetry metrics SDK integration with OTLP exporter support for gRPC and HTTP/protobuf protocols.

Motivation:
Enables customers to use the OpenTelemetry Metrics API and export metrics via OTLP to any compatible backend, including the Datadog Agent.

Change log entry
Adds OpenTelemetry metrics SDK integration with OTLP exporter support. Configure via DD_METRICS_OTEL_ENABLED and standard OpenTelemetry environment variables.

Key Features:

• OTLP exporter support (gRPC and HTTP/protobuf)
• Automatic endpoint resolution based on protocol and agent hostname
• Datadog service metadata mapped to OpenTelemetry resource attributes
• General OTLP settings (OTEL_EXPORTER_OTLP_*) as defaults for metrics-specific settings

Required Gems for metrics support:

• opentelemetry-metrics-sdk (~> 0.8)
• opentelemetry-exporter-otlp-metrics (~> 0.4)

Testing:

BUNDLE_GEMFILE=gemfiles/ruby_3.2_opentelemetry.gemfile bundle exec rspec spec/datadog/opentelemetry/metrics_spec.rb

[pr-commenter]

Benchmarks

Benchmark execution time: 2025-12-02 19:16:04

Comparing candidate commit ac5449b in PR branch munir/add-otel-metrics-configs with baseline commit 48fa3f2 in branch master.

Found 1 performance improvements and 0 performance regressions! Performance is the same for 43 metrics, 2 unstable metrics.

scenario:tracing - Propagation - Trace Context

• 🟩 throughput [+3422.995op/s; +3526.726op/s] or [+10.116%; +10.422%]

[ivoanjo]

Gave it another pass! I think this is getting in quite good shape :)

[mabdinur]

Gave it another pass! I think this is getting in quite good shape :)

Thanks so much for the thorough review and feedback. I really appreciate your time and patience. I learned a lot about ruby along the way 😸

[ivoanjo]

👍 Looks great to me! I really like how clean the tests ended up :)

[vpellan]

Requesting a change for the core/configuration/settings.rb file. Other requested changes are minor, after that it should be good !