Allow custom timeout value for webhook calls

[renan]

Because webhooks add to API request latency, they should evaluate as
quickly as possible. timeoutSeconds allows configuring how long the
API server should wait for a webhook to respond before treating the call
as a failure.

The default values from Kubernetes are, however, too large. For
admissionregistration.k8s.io/v1 the default value is 10 seconds while
for admissionregistration.k8s.io/v1beta1 is 30 seconds!

This custom/default value of 5 seconds should be more than enough for
standard installs.

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[bskiba]

Thanks, super useful. Can you set the default timeout to 30s? I know it's a ridiculously high value, but this is what the originally unconfigurable webhook timeout was set to and then the default behavior does not change unless users want to override it.

[renan]

@bskiba Makes sense. I amended my commit! :)

[renan]

The previously failing test has been now fixed 👍

[bskiba]

Thanks!
/lgtm
/approve

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[renan]

@bskiba Awesome, thank you! Oh, and it would be totally awesome if you could release a v0.8.1 or something. My clusters could use this feature 😅