Align CLI migrating with Group export/import integration
Once groups and projects are staged using the newly integrated Group export, group migrating will change. Instead of creating groups on destination, we will be exporting and importing the group structures before migrating projects (the usual way, using the Project export/import API).
As we handle project migration, groups should be multi-threaded as well. Project migration will not change and will start once all the groups and sub-groups have been migrated.
N.B. Remapping group user/member IDs may not be needed, if the group import matching is strictly based on email. Same applies to the Project export/import API, yet we were forced to remap the user/member IDs regardless, due to incidents in the past.