OCPBUGS-65828: Reduce log noise from transient async cache failures

[TheRealJon]

Summary

• Reduces excessive error logging in the console pod caused by transient OAuth endpoint timeouts
• Changes cache refresh error logging from ERROR to V(4) debug level in asynccache

Details

The console pod was flooding error logs with messages like:

failed a caching attempt: Get "https://kubernetes.default.svc/.well-known/oauth-authorization-server": context deadline exceeded

These are transient network failures that occur during periodic cache refreshes. The async cache:

• Retains the previous valid cached value when a refresh fails
• Automatically retries on the next refresh interval
• Successfully initializes during startup (when it does log at V(4) level)

This change aligns the periodic refresh error logging with the initialization behavior, reducing log noise while maintaining visibility at debug level.

Test Plan

• [x] Backend tests pass (./test-backend.sh)
• [x] Asynccache tests pass with 90% coverage
• [ ] Verify in cluster that error logs are reduced to V(4) debug level

Fixes: OCPBUGS-65828

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