[Feature Request] Add Harbor external storage configuration in VIC appliance

[tschwaller]

As an administrator I would like to configure external storage for the Harbor registry when deploying the VIC OVA (e.g. NFS Server, AWS S3, etc.), similar to how this is done with the Harbor Tile for VMware PKS. External storage gives the administrator better management capabilities.

If you run out of storage on the VMDK attached to the VIC/Harbor appliance, increasing it is a nontrivial task which can be avoided with external storage.

[zjs]

@renmaosheng: It looks like this issue has not been triaged. It may be related to or a duplicate of #1879.