feat(endpoints): rename behavior to outputs

"Outputs" is probably easier for most people to understand than "endpoints".

app/dts/behaviors/endpoints.dtsi

@@ -1,9 +0,0 @@
-/ {
-    behaviors {
-        end: behavior_endpoints {
-            compatible = "zmk,behavior-endpoints";
-            label = "ENDPOINTS";
-            #binding-cells = <1>;
-        };
-    };
-};

app/dts/behaviors/outputs.dtsi

@@ -0,0 +1,9 @@
+/ {
+    behaviors {
+        out: behavior_outputs {
+            compatible = "zmk,behavior-outputs";
+            label = "OUTPUTS";
+            #binding-cells = <1>;
+        };
+    };
+};