Honor stderrthreshold when logtostderr is enabled

[pierluigilenoci]

Summary

• After klog.InitFlags, opt into the fixed stderrthreshold behavior introduced in klog v2.140.0
• Bump k8s.io/klog/v2 from v2.130.1 to v2.140.0
• Applied to pkg/log/klogcontrol/klogcontrol.go (the init function that configures klog flags)

Motivation

When logtostderr is enabled (the default), klog historically suppressed the stderrthreshold flag, meaning that WARNING and ERROR messages could not be selectively filtered. klog v2.140.0 introduced new flags (legacy_stderr_threshold_behavior) to opt into the corrected behavior where stderrthreshold is properly honored.

Reference: kubernetes/klog#212

Test plan

• Verify the application still logs to stderr as expected
• Confirm stderrthreshold flag can be used to control which severity levels appear on stderr

[pierluigilenoci]

cc @klihub @fmuyassarov for review

[klihub]

@pierluigilenoci Thank you ! LGTM.

Is it so that all the dynamic controls we might exercise over klog when our configuration CR changes still works as before with the updated klog ?

[pierluigilenoci]

@klihub Thanks for the review and great question!

Yes, all dynamic controls over klog still work exactly as before. The legacy_stderr_threshold_behavior=false flag only changes how the stderrthreshold flag is interpreted at startup — it makes klog respect the configured threshold value instead of using a hardcoded legacy default.

Any runtime changes to klog verbosity levels (via klog.V() settings, flag changes, or your configuration CR) are unaffected. The flag is purely about the initial stderr threshold behavior, not about the dynamic control mechanism itself.

In short: this is a one-time startup flag that fixes the default behavior; all dynamic reconfiguration paths remain unchanged.