Update API docs to include namespaced Quizzes

Closes CNVS-12019

Test plan:

  - generate the API docs using `bundle exec rake doc:api`
  - verify that all the quiz APIs are included in the docs
  - verify that the appendices are functional (in the QuizSubmissions
    API for example)

Change-Id: I80c6a10c13777d0b88fe96a8114f25b9a2a6f007
Reviewed-on: https://gerrit.instructure.com/32490
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Derek DeVries <ddevries@instructure.com>
QA-Review: Myller de Araujo <myller@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>