fix(telemetry): improve support of conditions at the request level, especially for events

[bnjjj]

exists condition is now properly handled with events, this configuration will now work:

telemetry:
  instrumentation:
    events:
      supergraph:
        my.event:
          message: "Auditing Router Event"
          level: info
          on: request
          attributes:
            graphql.operation.name: true
          condition:
            exists:
              operation_name: string

Fixes #5702

Add warnings for invalid configuration on custom telemetry (PR #5759)

For example sometimes if you have configuration like this:

telemetry:
  instrumentation:
    events:
      subgraph:
        my.event:
          message: "Auditing Router Event"
          level: info
          on: request
          attributes:
            subgraph.response.status:
              subgraph_response_status: code # This is a first warning because you can't access to the response if you're at the request stage
          condition:
            eq:
            - subgraph_name # Another warning because instead of writing subgraph_name: true which is the selector, you're asking for a comparison between 2 strings ("subgraph_name" and "product")
            - product

This configuration is syntaxically correct but wouldn't probably do what you would like to. I put comments to highlight 2 mistakes in this example.
Before it was silently computed, now you'll get warning when starting the router.

---

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

• const - Basic stress test that runs with a constant number of users
• demand-control-instrumented - A copy of the step test, but with demand control monitoring and metrics enabled
• demand-control-uninstrumented - A copy of the step test, but with demand control monitoring enabled
• enhanced-signature - Enhanced signature enabled
• events - Stress test for events with a lot of users and deduplication ENABLED
• 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_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_callback - Stress test for events with a lot of users and deduplication ENABLED in callback mode
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• events_without_dedup_callback - Stress test for events with a lot of users and deduplication DISABLED using callback mode
• extended-reference-mode - Extended reference mode enabled
• large-request - Stress test with a 1 MB request payload
• no-tracing - Basic stress test, no tracing
• reload - Reload test over a long period of time at a constant rate of users
• step-jemalloc-tuning - Clone of the basic stress test for jemalloc tuning
• step-local-metrics - Field stats that are generated from the router rather than FTV1
• step-with-prometheus - A copy of the step test with the Prometheus metrics exporter enabled
• step - Basic stress test that steps up the number of users over time
• xlarge-request - Stress test with 10 MB request payload
• xxlarge-request - Stress test with 100 MB request payload

[BrynCooke]

I'm not sure I fully understand what's going on here. Let's talk.