feat(opentelemetry sink): add gRPC transport support

[thomasqueirozb]

Summary

Adds gRPC transport to the OpenTelemetry sink, complementing the existing HTTP transport. The sink now supports protocol.type = "grpc" using tonic over HTTP/2, with support for TLS, compression, batching, and retry logic matching the source's gRPC implementation.

Vector configuration

sinks:
  otel_grpc:
    type: opentelemetry
    inputs: [...]
    protocol:
      type: grpc
      endpoint: http://otel-collector:4317

How did you test this PR?

• Unit tests in src/sinks/opentelemetry/grpc.rs covering config parsing and URI scheme handling
• E2e test matrix extended with vector_grpc.yaml config (telemetrygen → OTel collector → Vector gRPC sink → OTel collector sink → file)
• Integration test in src/sinks/opentelemetry/integration_tests.rs (gated on opentelemetry-integration-tests feature) that sends OTLP log events to a live OTel collector via gRPC

Change Type

• Bug fix
• New feature
• Dependencies
• Non-functional (chore, refactoring, docs)
• Performance

Is this a breaking change?

• Yes
• No

Does this PR include user facing changes?

• Yes. Please add a changelog fragment based on our guidelines.
• No. A maintainer will apply the no-changelog label to this PR.

References

NA

[datadog-vectordotdev]

⚠️ Tests

✨ Fix all issues with Cursor

⚠️ Warnings

🧪 2 Tests failed

sinks::opentelemetry::grpc::tests::generate_grpc_config from vector (Datadog) (Fix with Cursor)

Test has failed

sinks::opentelemetry::grpc::tests::grpc_config_with_gzip from vector (Datadog) (Fix with Cursor)

Test has failed

ℹ️ Info

No other issues found (see more)

❄️ No new flaky tests detected

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