feat: Configurable audit log backend and policy

[dlipovetsky]

What problem does this PR solve?:
Allows user to configure the audit log backend, and policy.

Adds types to the cluster configuration that mirror the relevant kube-apiserver flags.

Introduces the auditlog handler. This handler patches the control plane kubeadm configuration template with flags, and the audit policy, based on the cluster configuration.

TODO

• Deploy the default audit policy as a ConfigMap in the controller namespace, so that it can be read and used in the patch. I like this, because it allows the user to configure the default policy. If the ConfigMap is not found, that would break cluster deployment, so that's a new risk. Open to ideas. We could continue to embed the default policy, for example.

Which issue(s) this PR fixes:
Fixes #

How Has This Been Tested?:

Special notes for your reviewer: