[postfix] Stouts.postfix

Created by: nemesisdesign

One patch still needs to be sent: https://github.com/nemesisdesign/Stouts.postfix/commit/3c42624da203e6f92cf340d8b828f0ec6feef181

Change the dependencies in meta/main.yml to use the latest Stouts.postfix role (instead of my fork, my patches have been merged months ago), remove my fork, install the main Stouts.postfix role in the local environment and test the installation again to ensure it works.