hass will ignore the standard SIGTERM sent by systemd during stop/restart and we
then have to wait for the timeout after which systemd will forcefully kill the
process.
If instead if we send SIGINT, hass will shut down nicely.
There are many issues reported upstream about the inability to shut down/restart
and it is *supposed* to work with SIGTERM but doesn't.
HA doesn't mind the configuration being JSON instead of YAML but since YAML is
the official language, use that as it allows users to easily exchange config
data with other parties in the community.
Additionally, some settings based on NixOS configuation is set via defaultConfig
which is then merged with the user provided configration.
For now that just means http port and time zone but others can easily be added.
