Feat/link external workitmes

[AlthausKonstantin]

Hello

we would like to have the ability to link work items that live in a different project.
Here is a proposal :)

[waynesun09]

The update on function with project_id support does not break backward comparability and test could pass.
The usage might be depend on user permissions which I did not verify or maybe it's not related.

Thanks for the contribution.