Load a private .env when present, but keep CI configuration in GitHub
runtime variables and retain the tracked template as a guide.

Keep latest as a main-branch alias while using Fedora/date versions for
image metadata and release tags.

Download and verify the selected release during image builds.
Bootstrap it once into the first graphical user's XDG directories.

Change IMAGE_NAEME to aerocore-os

Add build-time mirror configuration for Flatpak and Homebrew, expose the related build args, and install an AeroCore-owned profile script to load mirror environment files. Rename the mirror configuration files from the Bazzite-prefixed names to AeroCore-prefixed names while keeping the upstream Bazzite helper reference intact.

Verification: bash -n system_files/etc/profile.d/aerocore-mirrors.sh && bash -n build_files/build.sh

* refactor: rewrite in just, saner defaults

I think it makes sense to do this as it is longterm easier to maintain,
locally iterate and extend.

Documents how to rebase to a local image, it pains me greatly when
people iterate on github and wait forever for things to build and then
to download the image for trivial things they could also quickly do
locally.

Rpm-ostree rechunker by default instead of opt-in legacy-rechunker,
chunkah is also available if people want to use it already, if we deem
it ready then we can enable it later on. They can all be opted-out of.

Have a way to copy files to /{usr,etc} by default.

We should sign the digest of the image instead of the tag.

Co-Authored-by: a lot of sugar and bad music

* docs: bump fedora-bootc version

Co-authored-by: Jill Fiore <contact@lumaeris.com>

* fix: formatting inconsistency

Co-authored-by: Jill Fiore <contact@lumaeris.com>

* docs: remove variable mentions from workflows

These are now defined in the image-template.env file

* fix: small nits in labels

Co-authored-by: Adam Fidel <ledif@users.noreply.github.com>

---------

Co-authored-by: Jill Fiore <contact@lumaeris.com>
Co-authored-by: Adam Fidel <ledif@users.noreply.github.com>