feat: improve RedisCluster health check with retry and multi-node validation

[naimadswdn]

Description

• Retry health checks 3 times with exponential backoff
• Check all leader nodes instead of only leader-0
• Add better error handling and logging

Type of change

• New feature (non-breaking change which adds functionality)

Checklist

• Tests have been added/modified and all tests pass.
• Functionality/bugs have been confirmed to be unchanged or fixed.
• I have performed a self-review of my own code.
• Documentation has been updated or added where necessary.

Additional Context

Issue motivated by frequent E2E failure with Redis Cluster creation.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 34 lines in your changes missing coverage. Please review.
⚠️ Please upload report for BASE (main@1cc6cf1). Learn more about missing BASE report.

Files with missing lines	Patch %	Lines
internal/k8sutils/redis.go	0.00%	34 Missing ⚠️

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #1575   +/-   ##
=======================================
  Coverage        ?   32.13%           
=======================================
  Files           ?       79           
  Lines           ?     5844           
  Branches        ?        0           
=======================================
  Hits            ?     1878           
  Misses          ?     3782           
  Partials        ?      184           

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[drivebyer]

/lgtm