[2.18] disable auth webhook default

[cristicalin]

What type of PR is this?
/kind bug

What this PR does / why we need it:
When setting kubelet_authorization_mode_webhook: True kubespray creates extra kubernetes roles that might give kubelets more privileges than needed, allowing a compromised kubelet to elevate its privileges to cluster admin. We should set this to false by default.

Which issue(s) this PR fixes:

Fixes #

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

disable auth webhook default

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: cristicalin
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