use CRD defaults

[mateusoliveira43]

We should use CRD defaults to highlight what Non Admin objects default values are.

This would also fix problem around updating Non Admin object spec after velero object is created, so users can see the default values used (the fix for this is in Velero repository).

Similar issue with more details openshift/oadp-operator#1557

[mateusoliveira43]

Velero repository fix would need MutatingWebhookConfiguration, as default values are not static. But that would not give NAC the solution for free, as that would not be a marker in Velero object types

Example

User can change default TTL
https://github.com/vmware-tanzu/velero/blob/f02613d2f7a7cfbf687f84d1deac7414d679569e/pkg/cmd/server/config/config.go#L37
in CLI
https://github.com/vmware-tanzu/velero/blob/f02613d2f7a7cfbf687f84d1deac7414d679569e/pkg/cmd/server/config/config.go#L241

Possible fix

Try to automate the collecting of defaults applied by Velero
https://github.com/vmware-tanzu/velero/blob/f02613d2f7a7cfbf687f84d1deac7414d679569e/pkg/controller/backup_controller.go#L324
and apply them to NAC objects though our own MutatingWebhookConfiguration