utility function for "flush and exit"

[pohly]

/kind feature

Describe the solution you'd like

For the migration to structured logging, klog.Fatal is meant to be replaced with klog.ErrorS + os.Exit. However, that combination no longer flushes info messages.

We need a better recommendation and probably some new helper function in klog. For proposals, see kubernetes/kubernetes#107724 (comment)

[pohly]

We discussed this in WG Structured Logging and propose to
use this:

var ExitFlushTimeout = 10 * time.Second
klog.Errors(...)
klog.FlushAndExit(klog.ExitFlushTimeout, 255)