Allow to add interproject issue realtion
I suggest to allow to add relation issue from another project. Currently it is protected and form forbid to do it. (Or I do not know how enable this feature.) Some times projects have tree-like structure. And some related functional is need to be added to two or more projects. Or when functional is relocated from project to lib. Or it is making library extraction. Such work applied to multiple project at same time. The number of tasks is created for this purpose in each project.
Currently it is possible to make comment with links to related issues and projects in each related issue. But may be enable feature interproject task relation possible is better.