stats: auto-populate node.id and node.cluster in OTel stats sink resource

[Retr0-XD]

Problem

The OpenTelemetry stats sink emits metrics with an empty Resource (only telemetry.sdk.* attributes). Consumers such as OTel Collector processors have no way to identify which Envoy instance sent the metrics — making correlation of configs with metrics impossible.

Reported in #39931.

Solution

Automatically inject two resource attributes from LocalInfo when building the sink:

Attribute	Source	Example
node.id	LocalInfo::nodeName()	"envoy-pod-1"
node.cluster	LocalInfo::clusterName()	"my-service"

Priority rule: configured resource detectors take precedence — try_emplace ensures detector-set values are never overwritten.

Files changed

• source/extensions/stat_sinks/open_telemetry/config.cc — inject node.id/node.cluster before constructing OtlpOptions
• test/extensions/stats_sinks/open_telemetry/config_test.cc — factory smoke-test with non-empty node info + detector-priority test
• test/extensions/stats_sinks/open_telemetry/open_telemetry_impl_test.cc — end-to-end flush test verifying attributes appear in ResourceMetrics

Example config

No config change required. With the existing bootstrap:

node:
  id: envoy-pod-1
  cluster: my-service
stats_sinks:
- name: envoy.stat_sinks.open_telemetry
  typed_config:
    "@type": type.googleapis.com/envoy.extensions.stat_sinks.open_telemetry.v3.SinkConfig
    grpc_service:
      envoy_grpc:
        cluster_name: otel_collector

The exported ResourceMetrics.resource.attributes will now include:

node.id    = "envoy-pod-1"
node.cluster = "my-service"

---

AI disclosure: GitHub Copilot was used during implementation and test writing. I fully understand all changes made in this PR.

Commit Message: See PR title
Risk Level: Low
Testing: Unit tests added/verified
Docs Changes: N/A
Release Notes: N/A
Platform Specific Features: N/A

[repokitteh-read-only]

Hi @Retr0-XD, welcome and thank you for your contribution.

We will try to review your Pull Request as quickly as possible.

In the meantime, please take a look at the contribution guidelines if you have not done so already.

🐱

Caused by: #44066 was opened by Retr0-XD.

see: more, trace.