fix: Reduce CPU memory usage caused by Istio existence check

[jeffreylimnardy]

Description

Changes proposed in this pull request (what was done and why):

• Use client-go Discovery API instead of listing all CRDs in the cluster, which may cause CPU throttling issues in clusters with a lot of large CRDs.

Profiling results:

• Logs
  Before
  
  With Discovery API
  

• Metrics
  Before
  
  With Discovery API
  

• Traces
  Before
  
  With Discovery API
  

• Discovery API calls take on average 10 ms to complete

Changes refer to particular issues, PRs or documents:

• Istio status check CPU performance #1264

Traceability

• The PR is linked to a GitHub issue.
• The follow-up issues (if any) are linked in the Related Issues section.
• If the change is user-facing, the documentation has been adjusted.
• The feature is unit-tested.
• The feature is e2e-tested.