Update the string and action for battery saver notification

Update the strings and tapped action for the battery saver auto-turn-on
notification to make it clearer

Bug: 336960905
Flag: com.android.server.power.batterysaver.update_auto_turn_on_notification_string_and_action
Test: Manual Test

Change-Id: I38964a16a689ef0b887759c359d0412e5be9d306