feat: add Controller Internals Grafana dashboard

[rawadhossain]

Description

This PR adds the Controller Internals section, fifth of five planned dashboard sections for node-readiness-controller.

Questions it answers:

• Is the controller up and reachable?
• Is it keeping up with incoming reconcile work?
• Are workqueues building up or taking too long to process?
• Are reconciliations failing?
• Which controller version is currently running?

Most of these panels use metrics from controller-runtime and kube-state-metrics.

Panels in this Section

• Controller Up - controller availability.
• Workqueue Depth - queued reconcile work per controller.
• Workqueue Latency (p99) - p99 time items spend waiting in the queue.
• Reconcile Errors - failed reconcile attempts per second.
• Bootstrap Completions - total bootstrap completions since the controller started.
• Build Info - deployed version and pod identity.

Screenshot

Video demo

Section.5.mp4

Related to Issue #459

Type of Change

/kind feature

Testing

• Verified all panels render correctly against live data in a kind + kwok test cluster
• Confirmed the setup is reproducible from a clean cluster

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[kubernetes-prow]

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This pull-request has been approved by: rawadhossain
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[rawadhossain]

/cc @AvineshTripathi