[#69925732] Use vcloud-launcher configs in govuk-provisioning

vcloud-templates and vcloud-box-spinner are dead. This is a simpler version
of Nicola's yaml_input branch which:

- Uses the updated syntax of vcloud-launcher
- Only takes the required items out of each vApp entry
- Doesn't add disks - I'll create a separate story for that
- Removes support for JSON - we no longer need it

It will raise an error if you have an old `nodes.local.json` file.