Version Admiral upgrade script

[andrewtchin]

https://raw.githubusercontent.com/vmware/admiral/master/upgrade/src/main/resources/migrate.sh

As part of the OVA build we pull this script in. This should be versioned and released to a bucket on GCP so that we can have reproducible builds. Version name should match the name of the corresponding Admiral build artifact.

[andrewtchin]

Updated recommendations are to use an upgrade container for component upgrade https://github.com/vmware/vic-product/blob/master/installer/docs/DESIGN.md#appliance-upgrade-process
Please talk to me about how we can design this