Otherwise fall back to dockerfile-mode.
This also acts as an experiment of how to go about using the new Emacs
29.x treesit backed modes if available. This is currently not that
clean, but will do for now, and I'll keep experimenting with it.
I've taken a lot of inspiration from Emacs-Prelude when it came to the
structure of this rewritten config. I didn't want to use Prelude as I
don't agree with all it's defaults, nor do I want to have to deal with
any future changes in Prelude that might break things for me. So instead
I went down the fully custom path, but heavily inspired by Prelude, both
in terms of file/code structure, and also some of it's features.
Compared to my old config setup, it's got most of the same things, but
nearly everything is in a module file now, making it easy to fully
enable/disable certain features.
