Support for Compose v2

With the Compose specification [removing the requirement for the version field](https://github.com/compose-spec/compose-spec/pull/82) in a Compose file, Compose v2 and v3 syntax will be supported by the ACI integration. This is a work in progress but should arrive in the near future.

Initial question about this was posted here: https://github.com/docker/aci-integration-beta/issues/13