Fix global network warning while running ee shell

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.