Allow assignment of issues to upstream

When browsing the issues list users should be able to assign that bug to upstream. For example lets say the bug is caused by something upstream did like in this [https://trisquel.info/en/issues/4488 example issue]. They then patch it we should be able to assign the bug to upstream and in that case we know the patch will eventually make its way down to us. That way we know it isn't really a bug with Trisquel but something that the package developer should/needs to fix.

I think this should be implemented because a lot of times users report bugs here as bugs in Trisquel but in fact a lot of time it is simply a bug in that specific package which should be reported to the person writing that program.