For Terraform Cloud users using the 'remote' backend, the existing
'pattern' prompt should work just fine - but because their workspaces
are already present in TFC, the 'migration' here is really just
realigning their local workspaces with Terraform Cloud. Instead of
forcing users to do the mental gymnastics of what it means to migrate
from 'prefix' - and because their remote workspaces probably already exist and
already conform to Terraform Cloud's naming concerns - streamline the
process for them and calculate the necessary pattern to migrate as-is,
without any user intervention necessary.