Feature request: Add battery level indicator sample

@jaustin created this example for V1 that shows the current battery output as Volts on the display. 
https://os.mbed.com/teams/microbit/code/microbit-battery-test/

We surface this in 
https://support.microbit.org/solution/articles/19000069531-measuring-battery-capacity

Could we have a similar example using CODAL?