Replace start script with compose yaml

[andy5995]

docker-0ad-mod-testbed/start_0ad.sh

Line 8 in 9591fe5

docker run --rm -it \

Compose files are usually nicer than scripts. See https://docs.docker.com/compose/

[sl5net]

@wonderinglostsoul44 may you have fun to rejoin here?

[andy5995]

Some examples are at https://github.com/0ad-matters/0ad-appimage/blob/trunk/docker-compose.yml and
https://github.com/andy5995/linuxdeploy-build-helper-container/