cbatticon: Add support for batteryId

For devices with more than one battery, cbatticon allows to set the
battery ID as optional positional argument. If this argument is not
given, it default to the first battery it would list with `cbatticon
-p`. This commit adds support for the batteryId option to the cbatticon
module.

modules/services/cbatticon.nix

@@ -24,7 +24,7 @@ let
     ++ optional (cfg.updateIntervalSeconds != null)
     "--update-interval ${toString cfg.updateIntervalSeconds}"
     ++ optional (cfg.hideNotification != null && cfg.hideNotification)
-    "--hide-notification");
+    "--hide-notification" ++ optional (cfg.batteryId != null) cfg.batteryId);
 
 in {
   meta.maintainers = [ maintainers.pmiddend ];
@@ -94,6 +94,15 @@ in {
         default = null;
         description = "Hide the notification popups.";
       };
+
+      batteryId = mkOption {
+        type = types.nullOr types.str;
+        default = null;
+        description = ''
+          ID of the battery to monitor. List with {command}`cbatticon -p`.
+          Defaults to the first entry in the list.
+        '';
+      };
     };
   };