Switch default KCM --node-monitor-grace-period to 40s

[vlerenc]

What would you like to be added:

While introducing DWD, we set KCM's --node-monitor-grace-period to 120s, but this is very long and way beyond KCM's default of 40s. We should go back to that default, for seeds and shoots. See also gardener/dependency-watchdog#79.

Why is this needed:

We saw during "zone outage simulations" that recovery happens very slowly. It takes 2m for KCM to put a node into Unknown state and only then things move forward like endpoint and loadbalancer deregistration. Notable is especially our Istio ingress gateway/the API server that appears available for 2m before it gets updated even though it's dead for the entire time.

[timuthy]

Should we change the default setting to 40s with Kubernetes v1.27?
cc @ary1992

[acumino]

Completed in #7883
/close

[gardener-prow]

@acumino: Closing this issue.

In response to this:

Completed in #7883
/close

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