Behaviour for Mobius to check if the clock is set

On systems that need to set the time after boot events, metrics might report a nonsensical timestamp. Providing a clock implementation allows Mobius to make time adjustments on data received before the clock was set.

If no clock implementation is provided no time adjustments will be made.

For Nerves devices, NervesTime can be used to track time synchronization.

{Mobius, clock: NervesTime}

The time adjustments are best effort and might not be 100% exact, but this should only affect events that take place during the early stages of system boot.