Integrate Tails-specific Debian packages into the main git repo

We maintain some Debian packages which are solely used in Tails and cannot reasonably used outside of Tails. IMO, maintaining these as Debian packages makes our lives unnecessarily harder, because we have to release, build, and upload a new Debian package every time we change something in these packages.

We also share code between the main repo and some packages, which makes it hard to find usages/implementations.

The two packages I currently have in mind are tails-greeter and tails-persistence-setup.

I propose that we integrate them into the main git repo by copying the files that are installed by the package into config/chroot_local_includes.

Related issues

Is duplicate of #7036

Original created by @segfault on 16678 (Redmine)

To upload designs, you'll need to enable LFS and have an admin enable hashed storage. More information