### Steps to reproduce

* In the [documentation for the wysiwyg editor](https://www.openproject.org/docs/user-guide/wysiwyg/#available-attributes-for-work-packages), the `workPackageValue` macro lists all the available attributes.

### What is the buggy behavior?

* The attributes `startDate` and `dueDate` do not work for a work package of type milestone. One must use `date`, but it's not documented
* Example with milestone work package ##53565:
* `workPackageValue:53565:startDate` => workPackageValue:53565:startDate
* `workPackageValue:53565:dueDate` => workPackageValue:53565:dueDate
* `workPackageValue:53565:date` => workPackageValue:53565:date
* Example with bug work package ##53814:
* `workPackageValue:53814:startDate` => workPackageValue:53814:startDate
* `workPackageValue:53814:dueDate` => workPackageValue:53814:dueDate
* `workPackageValue:53814:date` => workPackageValue:53814:date

### What is the expected behavior?

* Begin of the insertionFor milestones
* startDate, dueDate and date result inEnd of the insertion Begin of the deletion The app behavior is correct (I suppose) but it should be documented thatEnd of the deletion the Begin of the insertionsame value (the one date value)
* For non-milestones
* startDateEnd of the insertion Begin of the deletion attributes `startDAte`End of the deletion and Begin of the insertiondueDate showEnd of the insertion Begin of the deletion `dueDate` do not work andEnd of the deletion that Begin of the insertionsingular date value
* date showsEnd of the insertion the Begin of the insertiondate range YYYY-MM-DD - YYYY-MM-DD
*End of the insertion Begin of the deletion attribute to be used is `date` for milestone work packages.End of the deletion