Include number of trades per aggregate window in snapshot all tickers request

[brigmecham]

The aggs endpoint returns a field called 'n' that has the number of trades in the interval.

The snapshot endpoint does not include this field. Is there a plan to include this field in the future? if not, could you?

It would make sense to add it as a field in the min sub object that is returned from the api request.

Thanks!

[matichenor]

This feature was also requested via polygon-io/issues#158 which I have consolidated into this ticket.