implement ifwait trigger service and use in bridge

should we convert all ifwait uses to this trigger too? seems
reasonable

modules/ifwait/default.nix

@@ -0,0 +1,18 @@
+{ config, pkgs, lib, ... } :
+let
+  inherit (pkgs) liminix;
+  inherit (lib) mkOption types;
+in {
+  options.system.service.ifwait =
+    mkOption { type = liminix.lib.types.serviceDefn; };
+
+  config.system.service.ifwait = config.system.callService ./ifwait.nix {
+    state = mkOption { type = types.str; };
+    interface = mkOption {
+      type = liminix.lib.types.interface;
+    };
+    service = mkOption {
+      type = liminix.lib.types.service;
+    };
+  };
+}