docs: Image Automation exclusions, OCI HelmRepository status, controller-runtime alerts

[RaviTharuma]

Fixes #2644. Fixes #2643. Fixes #2640. Operator docs for Alert exclusionList, OCI HelmRepository empty status, and controller_runtime_reconcile_errors_total alerts.

[Copilot]

🟡 Changes recommended

The troubleshooting cheatsheet change introduces a Markdown code-fence structure error that will break page rendering.

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Pull request overview

This PR updates Flux operator documentation to address common operational pain points: silencing transient Image Automation alert noise, clarifying OCI HelmRepository status/Ready column behavior, and providing Prometheus alerting examples based on controller-runtime error metrics.

Changes:

• Add an example PrometheusRule using controller_runtime_reconcile_errors_total for high-signal controller error alerting.
• Document Alert.spec.exclusionList patterns to exclude expected transient Image Automation errors (cold start / empty tag DB).
• Add troubleshooting guidance for OCI HelmRepository blank Ready/status and for Alert/Provider objects lacking status conditions.

File summaries

File	Description
content/en/flux/monitoring/metrics.md	Adds a controller-runtime reconcile error alerting section with a PrometheusRule example.
content/en/flux/monitoring/alerts.md	Adds Image Automation exclusionList examples and guidance to reduce noisy alerts.
content/en/flux/cheatsheets/troubleshooting.md	Documents OCI HelmRepository blank Ready/status behavior and Alert/Provider status limitations, with verification commands.

Review details

Suppressed comments (1)

content/en/flux/cheatsheets/troubleshooting.md:79

• There is an extra closing code fence (```) after the companion link which will break markdown rendering once the earlier code block is properly closed.

Companion: [notification-controller#1371](https://github.com/fluxcd/notification-controller/issues/1371).

- **Files reviewed:** 3/3 changed files
- **Comments generated:** 2
- **Review effort level:** Lite
</details>

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[RaviTharuma]

@matheuscscp re-review requested: applied your OCI/Alert wording, closed the kubectl fence before the OCI heading, removed the stray fence after the Alert companion, and used --kind=Alert. 27ceea7

[RaviTharuma]

@matheuscscp DCO is now signed on both commits (de95800 and e76e44c); the unsigned merge-from-main was dropped. Ready for re-review.