fix: honor -stderrthreshold when -logtostderr=true

[pierluigilenoci]

What

Bump klog to v2.140.0 and opt into the fixed behavior so that -stderrthreshold is respected even when -logtostderr=true (the default).

Why

klog v2 defaults -logtostderr to true. When active, the -stderrthreshold flag is silently ignored — all log severities are unconditionally written to stderr. This makes it impossible for log-aggregation systems to filter by severity.

This has been an open issue since 2020: kubernetes/klog#212

The fix was merged in klog v2.140.0 via kubernetes/klog#432 (authored by me) and introduces an opt-in flag legacy_stderr_threshold_behavior. Setting it to false enables the corrected behavior where -stderrthreshold is honored.

What changes

1. klog bumped from v2.80.1 to v2.140.0
2. In cmd/base/options/generic.go, after klog.InitFlags(local), two flags are set on the local FlagSet:
   • legacy_stderr_threshold_behavior=false — enables the fix
   • stderrthreshold=INFO — preserves current behavior (all severities still go to stderr by default)

Since these are set as defaults, users can now override -stderrthreshold=WARNING or -stderrthreshold=ERROR on the command line and it will actually work.

References

• Upstream issue: stderrthreshold not honored when logtostderr is set kubernetes/klog#212
• Upstream fix: feat: fix stderrthreshold not honored when logtostderr is set (#212) + two new flags kubernetes/klog#432

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