Allow lti_context_id to be returned with all assignment requests
Allow lti_context_id to be returned with all assignment requests

If the lti_context_id is used by an LTI tool to track an assignment,
the assignment endpoint will now return the lti_context_id
for symmetry with create requests, migrations and data services.

flag=none
Refs: QUIZ-9417

Change-Id: I9a5be25af7462960c0dc070b79cbcd95e759ba9d
Reviewed-on: https://gerrit.instructure.com/c/canvas-lms/+/289077
Tested-by: Service Cloud Jenkins <9144042a601061f88f1e1d7a1753ea3e2972119d@instructure.com>
Reviewed-by: Mark McDermott <20dd8ba615f2257ea7254f93d6f30ae11aa4f904@instructure.com>
QA-Review: Alex Slaughter <11669a22a05ead38ed9badafd55ef4c5386724b6@instructure.com>
Product-Review: Alex Slaughter <11669a22a05ead38ed9badafd55ef4c5386724b6@instructure.com>

sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms,sfu/canvas-lms