namespace quiz_submission_questions_controller under quizzes

fixes CNVS-11462
This commit moves QuizSubmissionQuestionsController into the Quizzes
namespace

Test plan
- Regression tests on the quiz submission questions api routes:
  - GET /api/v1/quiz_submissions/:quiz_submission_id/questions
  - GET /api/v1/quiz_submissions/:quiz_submission_id/questions/:id
  - PUT /api/v1/quiz_submissions/:quiz_submission_id/questions/:id
  - PUT /api/v1/quiz_submissions/:quiz_submission_id/questions/:id/flag
  - PUT
    /api/v1/quiz_submissions/:quiz_submission_id/questions/:id/unflag

Change-Id: Ia7c8a6c2833ffaa255c9eab2c6a36626fcbeddc5
Reviewed-on: https://gerrit.instructure.com/32945
Reviewed-by: Derek DeVries <ddevries@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Product-Review: Josh Simpson <jsimpson@instructure.com>