Make it possible to use Docker networking only

[betterphp]

We have a requirement to run multiple instances of rocket chat on one host.

With the current compose files we have to remove these two lines for that to work.

https://github.com/RocketChat/rocketchat-compose/blob/main/compose.database.yml#L17
https://github.com/RocketChat/rocketchat-compose/blob/main/compose.database.yml#L137

Changing the port numbers doesn't work as Mongo still uses its default port internally and that conflicts.

It would be great if there could be a .env var to control if the port mapping happens at all.