feat: add node_readiness_rules with enforcement_mode and dry_run labels

[rawadhossain]

Description

• Adds node_readiness_rules{enforcement_mode, dry_run} while keeping node_readiness_rules_total unchanged for compatibility.
• Updates the metric from the rule cache on rule create, update, and delete.
• Updates monitoring.md and docs/TEST_README.md.
• Adds related tests, also contributes to testing: Add Test Coverage for Prometheus Metrics #269.

from the design doc:

Related to #446

Type of Change

/kind feature

Testing

make test, make lint, go vet, gofmt -l all pass.

Checklist

• make test passes
• make lint passes

[kubernetes-prow]

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[kubernetes-prow]

Hi @rawadhossain. Thanks for your PR.

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[rawadhossain]

/cc @ajaysundark

[rawadhossain]

/cc @AvineshTripathi

[AvineshTripathi]

/ok-to-test

[rawadhossain]

/retest

[AvineshTripathi]

Since we're already calling ListRules in the collector, we can compute the enforcement_mode/dry_run breakdown there instead of maintaining a separate in-memory sync. The local ruleCache can lag behind actual cluster state and can be unreliable.

cc @ajaysundark wdyt?