What is the problem?
Currently decision instance reports are not creating a date histogram aggregation for date input/output variables, but instead use term aggregation, which does not make sense for date types.
Further, the default sorting of the result needs to be descending, similarly to OPT-2425.

What would be the expected behavior:
Date variables results are aggregated similarly to process instance date variables.
For sorting: Left is oldest date, right is newest date
Sorting should be the other way round - same as for group by start & end date

AT:

• group by (input/output) date variables returns date histogram aggregated results
• default sorting of group by input/output variables of type date for decision frequency reports should be descending
• the functionality should be tested properly in IT (as there is currently also no generated decision date variables)

Hint:
best make use of DmnModelGenerator introduced with OPT-2460 to create a dmn definition for testing