Add coprocessor metrics

[garypen]

Introduces a new metric for the router:

apollo.router.operations.coprocessor

It has two attributes:

coprocessor.stage: string (RouterRequest, RouterResponse, SubgraphRequest, SubgraphResponse)
coprocessor.succeeded: bool

Checklist

Complete the checklist (and note appropriate exceptions) before a final PR is raised.

• Changes are compatible[^1]
• Documentation[^2] completed
• Performance impact assessed and acceptable
• Tests added and passing[^3]
  • Unit Tests
  • Integration Tests
  • Manual Tests

Exceptions

Ran a router with all coprocessor stages enabled and prometheus enabled. Sent in a request to generate a success metric. Then stopped the coprocessor and sent in another request to generate a fail metric. Examined the prometheus metrics to ensure they were as expected. e.g.:

# HELP apollo_router_operations_coprocessor_total apollo.router.operations.coprocessor
# TYPE apollo_router_operations_coprocessor_total counter
apollo_router_operations_coprocessor_total{coprocessor_stage="RouterRequest",coprocessor_succeeded="false",service_name="apollo-router",otel_scope_name="apollo/router",otel_scope_version=""} 1
apollo_router_operations_coprocessor_total{coprocessor_stage="RouterRequest",coprocessor_succeeded="true",service_name="apollo-router",otel_scope_name="apollo/router",otel_scope_version=""} 1
apollo_router_operations_coprocessor_total{coprocessor_stage="RouterResponse",coprocessor_succeeded="true",service_name="apollo-router",otel_scope_name="apollo/router",otel_scope_version=""} 1
apollo_router_operations_coprocessor_total{coprocessor_stage="SubgraphRequest",coprocessor_succeeded="true",service_name="apollo-router",otel_scope_name="apollo/router",otel_scope_version=""} 1
apollo_router_operations_coprocessor_total{coprocessor_stage="SubgraphResponse",coprocessor_succeeded="true",service_name="apollo-router",otel_scope_name="apollo/router",otel_scope_version=""} 1

Notes

[^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.
- please raise a separate issue to automate the test and label it (or ask for it to be labeled) as manual test

[router-perf]

CI performance tests

• xxlarge-request - Stress test with 100 MB request payload
• step - Basic stress test that steps up the number of users over time
• events_without_dedup - Stress test for events with a lot of users and deduplication DISABLED
• events - Stress test for events with a lot of users and deduplication ENABLED
• 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.
• reload - Reload test over a long period of time at a constant rate of users
• xlarge-request - Stress test with 10 MB request payload
• 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

[BrynCooke]

Approved with suggestion

[BrynCooke]

Minor nit. Would be nice if these names matched the other use in the metrics naming.
e.g.
router.request, router.response etc rather than CamelCase.

[garypen]

I think we should monitor this and make the change in a followup PR if it seems sensible. Right now, the values are set to match the exact values transmitted in the coprocessor protocol. It would be nice to have some user feedback before changing.