16972 add assignee responsible to wp form

[``* `#16972` Support assignee/responsible property on work package forms and PATCH endpoint``](https://community.openproject.org/work_packages/16972)

Includes https://community.openproject.org/work_packages/17426

- [x] Path service
@ulferts fixed in https://github.com/opf/openproject/commit/9c33c168f4d9ad277fc40c4793bd15ba69c95f6e