This builds on #1064 by adding a JinjavaConfig value to turn off defaulting to the current date when a datetime filter is passed a null argument.

Instead it uses a fixed date, 2024-06-01, a potential deprecation date. I wanted a specific date so it was obvious that it was a default and not something like 0 which could be caused by other issues.

I'm going to find a way to make this date more configurable.