feeature(bt): Add "unpair combo" on startup.

* Especially for splits, we need the ability to
  unpair all paired devices as  sledgehammer
  if we need to "reset things", and doing so via
  keymaps isn't suitable.
* Allows shields to define a collection of key
  positions that if all held 2 seconds after
  startup, will unpair all existing pairs for the
  device.

app/Kconfig

@@ -40,11 +40,17 @@ menuconfig ZMK_BLE
 	select BT_PERIPHERAL
 	select BT_GATT_DIS
 	select BT_GATT_BAS
-	# select SETTINGS
-	# select BT_SETTINGS
+	select SETTINGS
+	select BT_SETTINGS
 
 if ZMK_BLE
 
+config ZMK_BLE_UNPAIR_COMBO
+	bool "Enable BT unpair combo"
+	help
+		Adds a magic key combo that can be held on startup to remove all paired devices
+	default n
+
 config ZMK_BLE_INIT_PRIORITY
 	int "Init Priority"
 	default 50