Document all pieces of the universal heartbeat

[PeterJohnson]

https://docs.wpilib.org/en/stable/docs/software/can-devices/can-addressing.html#universal-heartbeat is incomplete--it only documents byte 5 of the 8-byte frame.

[jasondaming]

Where is the rest of the information located? Is it information important enough / pertinent enough to document in frc-docs?

[Gold856]

The entire heartbeat was documented in #2269.