add lti ContentItemSelectionResponse message type

Test Plan:
  - install a tool with the message_type 'ContentItemSelectionResponse'
  - launch the tool
  - it should have the JSON param content_items
  - content_items should have a placementOf -> id that points to a migration API endpoint
  - run the migration by POSTing to the given endpoint
  - the migration should have all course content in it
  - try a migration with one assignment, one quiz, one module, and one page
    * add quizzes[]=:id&assignments[]=:id&modules[]=:id&pages[]=:id
  - the migration should only extract the specified items

closes CNVS-14613

Change-Id: Ic43c3fb1e77c12d5f4d6712d42932e63bc36762e
Reviewed-on: https://gerrit.instructure.com/39427
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Bracken Mosbacker <bracken@instructure.com>
Product-Review: Bracken Mosbacker <bracken@instructure.com>
QA-Review: Clare Strong <clare@instructure.com>