samples: drivers: can: add babbling node sample

In a Controller Area Network a babbling node is a node continuously (and
usually erroneously) transmitting CAN frames with identical - often high -
priority. This constant babbling blocks CAN bus access for any CAN frame
with lower priority as these frames will loose the bus arbitration.

Being able to simulate a babbling CAN node is useful when examining the
behavior of other nodes on the same CAN bus when they constantly loose bus
arbitration.

Signed-off-by: Henrik Brix Andersen <henrik@brixandersen.dk>