Bug 1941663: LTI submission: fix submittableto param to show release form

When groups are created  when submitting an assigment through an LTI
assignment, it needs to have submittableto=true for the release form to
show so that it can be graded and released.

Change-Id: Icdc055cc898cbde3605bb5814233008b021f3513
(cherry picked from commit 9d4f9dee)