Standardize time fields from DPA when API version updates

There are several time fields in DPA, some being

• spec.configuration.velero.args.backup-sync-period
• spec.configuration.velero.args.default-backup-ttl
• spec.configuration.velero.args.default-item-operation-timeout
• spec.configuration.velero.args.default-repo-maintain-frequency
• spec.configuration.velero.args.fs-backup-timeout
• spec.configuration.velero.args.garbage-collection-frequency
• spec.configuration.velero.args.item-operation-sync-frequency
• spec.configuration.velero.args.resource-timeout
• spec.configuration.velero.args.store-validation-frequency
• spec.configuration.velero.args.terminating-resource-timeout
• spec.configuration.nodeAgent.timeout
• spec.backupLocations[].velero.backupSyncPeriod
• spec.configuration.velero.defaultItemOperationTimeout
• spec.configuration.velero.resourceTimeout

And they are typed as string, metav1.Duration and time.Duration.

They should be all be the same type, for improved user and developer experience. They should also be validated in validators.

Start by tracing the listed DPA time fields through the API definitions and validators, comparing their current string, metav1.Duration, and time.Duration types across API versions. Done means the fields use a consistent type and validation is present for each affected field.