This solves problems on Linux distros like NixOS and BSDs like FreeBSD that don't provide `/bin/bash`, while also
maintaining support for all other distros out there (AFAIK? even Alpine with its Busybox has /usr/bin/env).
* Build: allow dynamically change docker image
Right now, only for couple DBs.
With the 2.1, you can do `${TAG:-5.6}` without needing the `.env` file, but
it seems it would be better for back-compat to support `.env` right now.
Fixes#17891
* Build: add prefix for removal process
* Docs: mention makefile command instead of the bash
Since we are moving to makefile for things and make command
simplifies some of the actions you have to perform to work with
different environments
* Docs: mention dynamic tags in the docs
* Docs: avoid name collision
Fixes#16107
