UserTask group by start/end date & distributed by assignee/candidate group

Context:
With OPT-2834, we created the first user task grouped by date reports. After some customer feedback, we realized that we still need to add the reports where the user can distribute the new user task reports by assignee/candidate group

AT:

• The following reports can be evaluated in the report builder:

  View	Grouped By	Distributed By
  User Task count	User Task start date	Assginee
  User Task count	User Task start date	Candidate Group
  User Task count	User Task end date	Assginee
  User Task count	User Task end date	Candidate Group
  User Task duration	User Task start date	Assginee
  User Task duration	User Task start date	Candidate Group
  User Task duration	User Task end date	Assginee
  User Task duration	User Task end date	Candidate Group

• the new reports are added to the user guide documentation