Add an option in DateTimeConverter (DateTimeFormat) to specify second precision

This thread outlines it pretty well:

https://community.safe.com/s/question/0D54Q00009QoujHSAR/best-way-to-remove-fractional-seconds-in-date-time

Currently if you want to drop the fractional component of seconds you need to do extra steps. This is fine, however, it feels like it would be neater it the DateTimeConverter/DateTimeFormat function could handle this.

Just a nice to have really.