docker: Investigate using separate networks for services

[ghost]

Is your feature request related to a problem? Please describe.

In the code review for the new docker / docker compose setup, it was suggested to use separate networks for the php services (see comment).

Describe the solution you'd like

Investigate if and how the services can be split into different networks. The www service should be externally accessible ( and maybe rabbitmq too?). The rest should be able to be shield off and only use the internal network.

Describe alternatives you've considered

N/A

Additional context

See docker compose networking documentation

[melroy89]

I think it's a must have to make this part of #1085.

So I will try to make this part of that PR and interoperate the changes there. Since if you expose all the ports to the external network it will interfere with existing services like PostgreSQL on the host machine. etc..