nixos/soft-serve: specify config path in env instead of systemd.tmpfiles

When config location is in systemd tmpfiles, if you nuke the
configuration directory (`rm -rf /var/lib/private/soft-serve`) and then
restart the service, the configuration file will not be set, and the
service uses default configurations. Having the configuration file in
env also removes the need to use 'restartTriggers'.

nixos/modules/services/misc/soft-serve.nix

@@ -45,11 +45,6 @@ in
 
   config = lib.mkIf cfg.enable {
 
-    systemd.tmpfiles.rules = [
-      # The config file has to be inside the state dir
-      "L+ ${stateDir}/config.yaml - - - - ${configFile}"
-    ];
-
     systemd.services.soft-serve = {
       description = "Soft Serve git server";
       documentation = [ docUrl ];
@@ -58,8 +53,7 @@ in
       wantedBy = [ "multi-user.target" ];
 
       environment.SOFT_SERVE_DATA_PATH = stateDir;
-
-      restartTriggers = [ configFile ];
+      environment.SOFT_SERVE_CONFIG_LOCATION = configFile;
 
       serviceConfig = {
         Type = "simple";