Fix global network warning while running ee shell

[kirtangajjar]

Getting following warning while running ee shell on a PHP site:

WARNING: Some networks were defined but are not used by any service: global-backend-network

This is occurring because a PHP site without DB or cache has global backend network in it's docker-compose.yml, but it's not used.

So to fix this issue, we need to add global backend network in docker-compose.yml only when --cache or --with-db flag is passed.