[CBM] Add support for resuming restores

At the moment, cbbackupmgr doesn't support resuming restores; if a restore fails midway through, you must start from the beginning and rely on conflict resolution.

For large restores it makes sense to be able to resume restoring similar to how we support resuming backups.

This will be an important addition for cloud restore because a restore could fail for a multitude of different environmental reasons and we know that pulling data from S3 is far more expensive than uploading.

This may become quite important for collection aware restores now that cbbackupmgr auto-remaps scopes/collections it creates. Lets imagine this case (which can currently happen):
1) User backs up a collection aware cluster (that has a decent amount of collections).
2) User deletes/flushes target bucket
3) User then restores to the target bucket (cbbackupmgr creates all the scopes/collections)
4) cbbackupmgr crashes/errors out for some reason
5) User attempts to continue the restore
6) cbbackupmgr will complain/error out stating that scopes/collections exist on the target cluster with a different id than in the backup.

This is extremely inconsistent and likely would be confusing to users e.g. why would it moan this time, and not when they first started the restore. Obviously, that's logical to cbbackupmgr since the plan is not persisted on a restore (meaning, the second time they try the restore, we have no way of knowing that we created those collections).