home-assistant: use SIGINT instead of SIGTERM to shut down (#49571)

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.

nixos/modules/services/misc/home-assistant.nix

@@ -157,6 +157,7 @@ in {
         Restart = "on-failure";
         ProtectSystem = "strict";
         ReadWritePaths = "${cfg.configDir}";
+        KillSignal = "SIGINT";
         PrivateTmp = true;
         RemoveIPC = true;
       };