Timesheet: Automatically split weeks that pass a month-line

[#1]

As an admin, I can set that an auto-created timesheet cannot include two different months, so that I can ensure a clear monthly closing of the financial data.

A timesheet is automatically created for one week. If the end of a month falls within that period, the expectation would be that two timesheets are created, one covering the part of the week within the first month, the other the rest. E.g. 29.03.21 - 04.04.21 would result in Timesheet 1: 29.03.21-31.03.21 and Timesheet 2: 01.04.21-04.04.21