16983 api extend wp patch for description

[``* `#16983` Extend API V3's work package PATCH endpoint for description``](https://community.openproject.org/work_packages/16983)
So sad we have to wait for the next reform version to be published: https://github.com/apotonick/reform/issues/117. Let's talk about using an unstable version of reform or taking 1.1.1 (or 1.0.4) and putting the Dirty feature on it. It would be a bet though, to have be able to remove it until 4.1 is released.