Injecting configuration specific dependencies into the
propagatedBuildInputs of the home-assistant package forces alot of
rebuilds while setting up home-assistant, which is annoying.
By passing optional dependencies into home-assistant via the systemd
units PYTHONPATH environment variable, only he concatenation of
library paths in the systemd unit requires a rebuild.
This also means users can rely heavily on the cached home-assistant
package and will rarely have to build from source, if ever.
e01ccd6245