Switch from docker to podman

It would be an enhancement to say goodbye to docker, and welcome podman

Pros:

• Technical reasons
  • containers can be run as a non-root user ¹
  • no single daemon
  • better integrates with already-existing linux parts
  • mostly compatible with docker
• Roundabout reasons:
  • Although one of the requirements for self-hosting ecloud is Ubuntu, that is an overly strict one - I managed ² to install the server on openSUSE Leap 15.1, and I reckon there are others who have similar distate for deb-based distros.
    And RedHat just removed non-enterprise docker from its repos, so we cannot recommend /e/ self-hosting to Fedora/RHEL/etc userbase.
  • Recent acquisition and continuous investor hunting of Docker company is a bit concerning.

Cons:

• systemd unit files probably must be written, as podman unit file generator is not good enough

1. port handling has some issues in case when run as non-root ↩

2. well, almost, nextcloud and onlyoffice container needs some fixing ↩