Optimize k8s client creation for snapshot limit checks

[deepakkinni]

What this PR does / why we need it:
This PR optimizes the Kubernetes client creation in the WCP CSI controller by initializing it once during controller startup instead of creating a new client on every snapshot operation. This reduces performance overhead, memory allocations, and API server load.

Which issue this PR fixes (optional, in fixes #<issue number>(, fixes #<issue_number>, ...) format, will close that issue when PR gets merged): fixes #

Testing done:
Precheckins(WCP) PASS: https://jenkins-vcf-csifvt.devops.broadcom.net/job/wcp-instapp-e2e-pre-checkin/846/
Precheckins(VKS) PASS: https://jenkins-vcf-csifvt.devops.broadcom.net/job/vks-instapp-e2e-pre-checkin/786/

All existing unit tests pass (TestGetSnapshotLimitForNamespace and TestGetPodVMUUID)

No linter errors

Verified that the k8s client is initialized once during controller Init() and reused across all getSnapshotLimitForNamespace calls


Running Snapshot Limit Enforcement Tests
========================================

Category: Basic Limit Enforcement
-----------------------------------
  ✓ Test #1: Create Within Limit (5/10) - PASSED (12s)
  ✓ Test #2: Exceed Limit (11/10) - PASSED (8s)
  ✓ Test #7: Absolute Max Enforcement (33/32) - PASSED (10s)
  ✓ Test #14: Zero Limit Config - PASSED (2s)

Category: ConfigMap Configuration
---------------------------------
  ✓ Test #3: No ConfigMap Present - PASSED (5s)
  ✓ Test #4: Invalid ConfigMap Value - PASSED (3s)
  ✓ Test #5: Per-Class Limits - PASSED (15s)
  ✓ Test #6: Missing Snapshot Class Key - PASSED (8s)
  ✓ Test #10: Empty ConfigMap - PASSED (2s)

Category: Snapshot Counting
---------------------------
  ✓ Test #8: Cross-PVC Counting (2 PVCs) - PASSED (18s)
  ✓ Test #9: Deleted Snapshots Don't Count - PASSED (20s)
  ✓ Test #11: Multiple Classes (2 classes) - PASSED (22s)
  ✓ Test #12: Failed Snapshots Count - PASSED (12s)
  ✓ Test #13: Pending Snapshots Count - PASSED (10s)

Category: Cleanup & Resource Management
---------------------------------------
  ✓ Test (implicit): Resource cleanup - PASSED
  ✓ Test (implicit): PVC deletion order - PASSED
  ✓ Test (implicit): Namespace isolation - PASSED

========================================
Test Results: 14/14 PASSED

Test Link: https://gist.github.com/deepakkinni/faa1c69b3f21ffeb3843011b60fad7ee

Special notes for your reviewer:

Release note:

Optimize Kubernetes client creation in WCP CSI controller by initializing once at startup instead of per-snapshot operation

[deepakkinni]

FAILED --- Jenkins Build #842

[deepakkinni]

Triggering CSI-TKG Pre-checkin Pipeline for this PR... Job takes approximately an hour to complete
Jenkins Build #784

[deepakkinni]

Triggering CSI-TKG Pre-checkin Pipeline for this PR... Job takes approximately an hour to complete
Jenkins Build #785

[deepakkinni]

Triggering CSI-TKG Pre-checkin Pipeline for this PR... Job takes approximately an hour to complete
Jenkins Build #786

[deepakkinni]

SUCCESS --- Jenkins Build #846

[xing-yang]

Can you add your pre-check pipeline link to the PR description?

[xing-yang]

/approve

[divyenpatel]

/approve
/lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: deepakkinni, divyenpatel, xing-yang

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