feat(display): Add new peripheral status/display

* Add new API/status to track state of the
  peripheral connection to the central.
* Add new peripheral status widget for displaying
  the current status of the connection to
  the central.

app/src/events/split_peripheral_status_changed.c

@@ -0,0 +1,10 @@
+/*
+ * Copyright (c) 2022 The ZMK Contributors
+ *
+ * SPDX-License-Identifier: MIT
+ */
+
+#include <kernel.h>
+#include <zmk/events/split_peripheral_status_changed.h>
+
+ZMK_EVENT_IMPL(zmk_split_peripheral_status_changed);