Checks error for loading audit webhook config to prevent panic

[JoshVanL]

Signed-off-by: JoshVanL vleeuwenjoshua@gmail.com

What type of PR is this?
/kind bug

What this PR does / why we need it:
This PR prevents the apiserver from panicking when failing to load the audit webhook config (i.e. when the ca file cannot be read).

Which issue(s) this PR fixes:

Fixes #88878

Special notes for your reviewer:

Does this PR introduce a user-facing change?:

FIX: prevent apiserver from panicking when failing to load audit webhook config file

Additional documentation e.g., KEPs (Kubernetes Enhancement Proposals), usage docs, etc.:

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[k8s-ci-robot]

Hi @JoshVanL. Thanks for your PR.

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[liggitt]

/lgtm
/approve
/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: JoshVanL, liggitt

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Needs approval from an approver in each of these files:

• staging/src/k8s.io/apiserver/plugin/pkg/audit/OWNERS [liggitt]

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[RA489]

/test pull-kubernetes-e2e-kind
/test pull-kubernetes-e2e-gce

[munnerz]

/priority important-soon

[dims]

this is a bug and the trace back with panic does not help. let's fix this in 1.18.

/milestone v1.18

[liggitt]

/retest