Use new transversal directory structure

[wget]

Just following Docker default images recommendations.

My idea is to bring the same workflow as does Docker Inc with their official images.

i.e. a transversal commits instead of branches, the way they perform is to use folder with the different versions supported. My idea was to have Dockerfile and Docker Compose (V2) files for Mautic 2.x, 3.x and 4.x.

example with the official MariaDB Docker container:

• https://github.com/docker-library/official-images/blob/master/library/mariadb
• https://github.com/MariaDB/mariadb-docker

Indeed even if Mautic 2 and 3 aren't supported any more by Mautic, a bunch of companies are in the need of Dockerizing the current version they have. This was the case with Collabora. We had a version running behind our firewalls and we Dockerized it right away.

[RCheesley]

As I understand it @wget this will be a backwards compatibility breaking change for folks who are already using the Docker image, is that correct?

@luizeof @fedys would you be able to take a look and share your thoughts / review as appropriate?

@wget we will definitely need this to be documented. Can you make a PR to https://github.com/mautic/mautic-documentation to add this in the 'installing with Docker' section, and also if possible to the new end-user docs at https://github.com/mautic/user-documentation as well (note the latter uses RST, happy to help if you need any assistance with that).

Thanks!

[wget]

@RCheesley There won't be any compatibility breaking changes with what the users USING the Docker containers will see.

The changes are basically from our side, the devops writing the Dockerfile and docker-compose.yml. These will be reorganized to match Docker Inc best practices, nothing more :)

Yes, I'll document this right away via a PR on the documentation side (I'm used to usr Restructured text at Mattermost Inc and Collabora Productivity, no news from me, but thanks for the offer) =)