feat(behaviors): Add behavior metadata information.

* For upcoming ZMK studio work, make a set of rich metadata available
  to provide a friendly name for a behavior, and allow super flexible
  descriptions of the parameters the behaviors take.
* Add ability to validate a zmk_behavior_binding against
  the behavior metadata available.

app/dts/behaviors/key_repeat.dtsi

@@ -12,6 +12,7 @@
             compatible = "zmk,behavior-key-repeat";
             #binding-cells = <0>;
             usage-pages = <HID_USAGE_KEY>;
+            display-name = "Key Repeat";
         };
     };
 };