Add support of instruments in configuration for telemetry

[bnjjj]

Add support for custom and standard instruments through the configuration file. You'll be able to add your own custom metrics just using the configuration file. It can be conditional, get values from selectors like headers, context, body. And the metrics can have different types like histogram or counter.

Example:

telemetry:
  instrumentation:
    instruments:
      router:
        http.server.active_requests: true
        acme.request.duration:
          value: duration
          type: counter
          unit: kb
          description: "my description"
          attributes:
            http.response.status_code: true
            "my_attribute":
              response_header: "x-my-header"
  
      supergraph:
        acme.graphql.requests:
          value: unit
          type: counter
          unit: count
          description: "supergraph requests"
          
      subgraph:
        acme.graphql.subgraph.errors:
          value: unit
          type: counter
          unit: count
          description: "my description"

Documentation

Fixes #4319

---

Checklist

Complete the checklist (and note appropriate exceptions) before the PR is marked ready-for-review.

• Changes are compatible¹
• Documentation² completed
• Performance impact assessed and acceptable
• Tests added and passing³
  • Unit Tests
  • Integration Tests
  • Manual Tests

Exceptions

Note any exceptions here

Notes

Footnotes

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. ↩

2. Configuration is an important part of many changes. Where applicable please try to document configuration examples. ↩

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

[router-perf]

CI performance tests

• reload - Reload test over a long period of time at a constant rate of users
• events_big_cap_high_rate_callback - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity using callback mode
• events_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
• large-request - Stress test with a 1 MB request payload
• const - Basic stress test that runs with a constant number of users
• no-graphos - Basic stress test, no GraphOS.
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• events - Stress test for events with a lot of users and deduplication ENABLED
• events_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
• events_big_cap_high_rate - Stress test for events with a lot of users, deduplication enabled and high rate event with a big queue capacity
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• xxlarge-request - Stress test with 100 MB request payload
• xlarge-request - Stress test with 10 MB request payload
• step - Basic stress test that steps up the number of users over time

[BrynCooke]

One thing that needs to be added are the config metrics in configuration/metrics.rs. It can use the same pattern as we did for spans.

[BrynCooke]

In general this is looking good.

I think that the code very unit testable so would like to see the individual functions tested in each module.

[BrynCooke]

I think default_attribute_requirement_level is not working quite right. I had a poke around and didn't manage to spot the issue in the code.
Here's my config:

telemetry:
  exporters:
    metrics:
      prometheus:
        enabled: true
  instrumentation:
    instruments:
      default_attribute_requirement_level: recommended
      router:
        http.server.request.duration:
          attributes:
            network.protocol.version: true

I was expecting the recommended attributes to appear on the standard instrument but there are none:
http_server_request_duration_bucket{otel_scope_name="apollo/router",le="0.001"} 0

Note also that the standard attributes do not correlate with the span standard attributes, so if we're sharing logic there then it'll add the wrong attributes.