Add docker sub-template

[MrTango]

We want a sub-template to build pre configured docker container, which contain a custom Plone installation including all needed extensions. The template should be able to create a standalone container or a zeo-setup which uses Docker compose to setup multible docker container (zeo-client, zeo-server).

See this conversation where the idea started. https://community.plone.org/t/gsoc-2018-ideas-plone-cli-docker-support/5287/8 https://community.plone.org/t/docker-and-plone-for-add-on-development/5094/4 also at the docs here: https://github.com/plone/plone.docker/tree/master/docs

[pigeonflight]

The key capability that I'd like to see is to be able to transform a buildout into a "docker compatible buildout" with a simple command

plonecli dockerize

Take a look at: https://docs.google.com/document/d/1E4A2X9-3ypSJXOKElfl-XIwyO0OpjhFv-geZFPWUSqA/edit#heading=h.x2b3meayykxy

[MrTango]

@pigeonflight so the purpose is using docker containers for development right? By a buildout created by plonecli, you mean the self contained buildout of the addon template right? Or do you want to inlcude multible packages into the container? But then we would to use the buildout template for the base strucure and then include all needed packages there.