refactor(hooks): discover kube feature gates via metrics endpoint

[yaroslavborbat]

Description

Refactored the discover-kube-apiserver-feature-gates hook to discover enabled feature gates
by scraping the kube-apiserver /metrics endpoint instead of parsing the kube-apiserver pod's
command-line arguments (--feature-gates=...).

Key changes:

• Removed the Kubernetes watch on kube-apiserver pods and the associated JqFilter snapshot logic.
• Added fetchMetrics — fetches raw Prometheus metrics from /metrics via the REST client.
• Added parseEnabledFeatureGates — parses kubernetes_feature_enabled{...} 1 lines to extract enabled gate names.
• Fixed draFeatureGatesPath condition: DRAResourceClaimDeviceStatus was previously assumed always enabled; it is now explicitly checked.
• Added unit tests covering parseEnabledFeatureGates and the full reconciliation flow with a mock HTTP server.

Why do we need it, and what problem does it solve?

The previous implementation parsed the --feature-gates CLI flag from the kube-apiserver pod spec.
This approach is fragile: it only captures explicitly set gates and misses all gates that are
enabled by default (i.e., those not listed in the flag). This caused incorrect detection of DRA
feature gates in environments where gates are enabled by default without being explicitly passed
to the API server.

The /metrics endpoint exposes kubernetes_feature_enabled gauge for all known feature gates,
including defaults, giving a complete and authoritative picture of what is actually enabled at runtime.

What is the expected result?

1. Deploy the module in a cluster where DRA feature gates are enabled by default (not via --feature-gates).
2. Observe that virtualization.internal.kubeAPIServerFeatureGates is correctly populated with
   all enabled gates.
3. Observe that virtualization.internal.hasDraFeatureGates is set to "true" when
   DRAResourceClaimDeviceStatus, DRADeviceBindingConditions, and DRAConsumableCapacity are all enabled.

Checklist

• The code is covered by unit tests.
• e2e tests passed.
• Documentation updated according to the changes.
• Changes were tested in the Kubernetes cluster manually.

Changelog entries

section: vm
type: fix
summary: Stabilized the operation of USB devices for virtualization on Deckhouse version ≥1.76 and Kubernetes version ≥1.33.