Using Counter variable doc update - regd Nudges

[tanuprasad530]

One of the use cases mentioned here is using contact variables to track nudges. Because Nudges are flow specific, using contact variables may be not be the most optimal approach to track nudges.

This should be tracked using result variables, by saving the result for each nudge and then performing a split by to check if the last nudge has been sent. Need to update this doc/add a new documentation for nudges.