In #89806 it has been reported that the final package is missing a lot
of features like support for the self-service GUI and the
config-management.
While working on supporting those components in the Nix-package, I
decided to refactor the package to simplify the entire setup.
This patch changes the following things:
* Binaries and libraries are patched using the `autoPatchelfHook` to
avoid having unneeded libraries linked (e.g. some programs use gtk2,
others use gtk3).
* Moved source-declarations into their own file.
* Wrapped `configmgr` and `selfservice` and added those to `$out/bin`.
* Don't mention the old `citrix_receiver`-packages in the manual anymore
since those packages were removed in 19.09 and are EOLed anyways.
Closes #89806
