docs: add circuit breaker metrics counters

[mfkd]

Summary

• document the three XR circuit breaker Prometheus counters alongside the existing Crossplane metrics table

Related issues

• Fixes crossplane/crossplane#6850
• PR crossplane/crossplane#6854

Testing

• I ran hugo server and ensured it formats correctly

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[mfkd]

Thanks @jbw976. I’ve pushed your requested changes.

Namely:

1. DSO sign off
2. Updated the circuit breaker metrics from crossplane_circuit_breaker_* to circuit_breaker_* to reflect the refactor changes in crossplane/crossplane#6870

While reviewing the metrics docs, I noticed gaps around engine, function-runner, and cached-runner metrics. The docs appear to list only one histogram metric and omit related counters/gauges, which may make it harder for users to discover all available metrics. Is this intentional for now?

Code references: • Engine metrics — not currently listed in metrics.md • Function runner metrics — only run_function_seconds histogram appears to be documented. Also the documentation has not been updated to reflect the naming change made here • Cached runner metrics — not currently listed in metrics.md

From what I can tell, the documented metrics mainly cover those exposed by controller-runtime, client-go, and some implemented in crossplane-runtime but omits much of the metrics mentioned above in crossplane/crossplane.

Would it make sense to open follow-up PRs to document these missing metrics in metrics.md, or is there existing work covering this?

[jeanduplessis]

@mfkd I don't believe we intentionally are leaving out the missing metrics you mention. If you're willing to add them in a follow up PR that would be appreciated.

[mfkd]

@jeanduplessis Thanks! I’ll get to it sometime next week.