Add ability to expose ports instead of publish them.

[Renari]

This would allow you to use a reverse proxy to publish instead of exposing ports on the host for every application.

[stavros-k]

I think an option to just not publish them to host (per port) should be enough.
expose is not really doing something, its mostly informative.

https://docs.docker.com/reference/dockerfile/#expose

That being said, this option would only make sense if there is also custom network support.
(Correct my if I'm wrong) But 2 services in different stacks cannot communicate internally unless they are joined on the same custom network.

[Renari]

(Correct my if I'm wrong) But 2 services in different stacks cannot communicate internally unless they are joined on the same custom network.

I do believe that to be true, which is why #743 was also opened.