fix(telemetry): export properly resources configured on prometheus

[bnjjj]

When configuring resource to globally add labels on metrics like this:

telemetry:
  apollo:
    client_name_header: name_header
    client_version_header: version_header
  exporters:
    metrics:
      common:
        resource:
          "test-resource": "test"
      prometheus:
        enabled: true
        resource_selector: all # This will add resources on every metrics

test-resource label was never exported to prometheus, this bug only occurs with prometheus and not otlp.
This PR fixes this behavior and will no longer filter resources.

---

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• Changes are compatible¹
• Documentation² completed
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• Tests added and passing³
  • Unit Tests
  • Integration Tests
  • Manual Tests

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1. It may be appropriate to bring upcoming changes to the attention of other (impacted) groups. Please endeavour to do this before seeking PR approval. The mechanism for doing this will vary considerably, so use your judgement as to how and when to do this. ↩

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3. Tick whichever testing boxes are applicable. If you are adding Manual Tests, please document the manual testing (extensively) in the Exceptions. ↩

[svc-apollo-docs]

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File Changes

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* graphos/routing/(latest)/observability/telemetry/metrics-exporters/prometheus.mdx

Build ID: 2a5812e2b6ed7af8c5659ab8

URL: https://www.apollographql.com/docs/deploy-preview/2a5812e2b6ed7af8c5659ab8

[BrynCooke]

I'm not clear this is the best way to go, usually target_info has the resource info:

# HELP target_info Target metadata
# TYPE target_info gauge
target_info{process_executable_name="router",service_name="unknown_service:router",service_version="2.2.1",test="test"} 1

https://opentelemetry.io/docs/specs/otel/compatibility/prometheus_and_openmetrics/#resource-attributes-1

[BrynCooke]

I think all that's needed is that this is a config option in the prometheus config. Here's the relevant part of the spec:

In Prometheus exporters, an OpenTelemetry Resource SHOULD be converted to a target info metric if the resource is not empty. The Resource attributes MAY be copied to labels of exported metric families if required by the exporter configuration, or MUST be dropped. The target info metric MUST be an info-typed metric whose labels MUST include the resource attributes, and MUST NOT include any other labels.

So to merge the PR is to move away from the "SHOULD" behaviour.

We can add an option on the prometheus exporter for this to fulfil: The Resource attributes MAY be copied to labels of exported metric families if required by the exporter configuration

[BrynCooke]

Suggest:

telemetry:
  exporters:
    metrics:
      prometheus:
        enabled: true
        resource_selector: all

[bnjjj]

@BrynCooke Still unsure to understand because if I set this configuration to false I have no way to export the resources mentioned in the config. I think I'll just get rid of ResourceSelector::All and use RessourceSelector::KeyAllowList (https://docs.rs/opentelemetry-prometheus/latest/opentelemetry_prometheus/enum.ResourceSelector.html#variant.KeyAllowList) it would cause less issues

[BrynCooke]

You just need to add docs for the new option