feat(shields): Make settings_reset shield reset all settings

Added a new CONFIG_ZMK_SETTINGS_RESET_ON_START option which enables init
code to call zmk_settings_erase(), and changed the settings_reset shield
to use it instead of CONFIG_ZMK_BLE_CLEAR_BONDS_ON_START, so it now
resets all settings instead of just clearing BLE bonds.

CONFIG_ZMK_BLE_CLEAR_BONDS_ON_START is left in place for now in case
someone still needs it. It may be replaced in the future once we find a
better way to repair a broken split connection.

app/Kconfig

@@ -565,6 +565,9 @@ endmenu
 
 if SETTINGS
 
+config ZMK_SETTINGS_RESET_ON_START
+    bool "Delete all persistent settings when the keyboard boots"
+
 config ZMK_SETTINGS_SAVE_DEBOUNCE
     int "Milliseconds to debounce settings saves"
     default 60000