Not compatible with Docker 5.0.0

[NeillM]

Our automatic testing server appears to have upgraded to docker 5.0.0 from the older docker 2.x line and now the moodle-docker-compose script no longer starts things.

It tries to fallback from docker compose to docker-compose (which is no longer present)

[paulholden]

It's Docker compose that causes the version incompatibility - will be fixed by #342