Rewrite related MRs widget with Vue
This MR rewrites existing Related Merge Requests widget with Vue with reusing shared Related Issues components.
With this MR we will also show MR assignees and milestone information in the widget.
There is also a follow-up issue to fix spacing issues with the Related MRs and Issues widgets.
Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/57662 and fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/58926
Edited by Fatih Acet