Check user permissions to determine if "Reopen merge request" should be displayed

Right now on Closed Merge requests, the "Merge request actions" menu shows the menu item "Reopen merge request" any time the user is authenticated.

If the authenticated user cannot perform the Reopen action (e.g. if they are not a part of the project), clicking this menu item leads to a 404 page.

We should add a check to this menu item to determine if it should be shown to the authenticated user.

(Unauthenticated users do not see the "actions" menu at all)