Defaulting webhook for enforced Velero Backup/Restore spec in NAB/NAR spec

[mateusoliveira43]

With #37, admin users will be able to enforce Velero Backup/Restore spec in NonAdminBackup/Restore spec fields. For better non admin users experience, would be good to apply the enforced NonAdminBackup/Restore spec fields as defaults. To do this, we need to create a defaulting webhook.

To do that, we need to run

kubebuilder create webhook \
    --plugins go.kubebuilder.io/v4 \
    --group nac \
    --version v1alpha1 \
    --kind NonAdminBackup \
    --defaulting
make manifests

and update docs/architecture.md. Reference https://book.kubebuilder.io/cronjob-tutorial/webhook-implementation

Note: would be better to update kubebuilder version prior to this work.

We also need to update NAC Deployment in OADP and deploy a NAC Service and NAC MutatingWebhookConfiguration

[mpryc]

@mateusoliveira43 will this webhook be part of non-admin backup or installed via oadp operator?