fix documentation issues for quiz extensions api

fixes CNVS-13237

test plan:
  - generate the documentation for the api
    - the description for the endpoint to set extensions has been corrected
    - the copyright block is no longer in the docs
    - user_id is now correctly described as 'Required' instead of 'Optional'
    - The attributes of the QuizExtension object description have been changed
      to not show the extend_from_now and extend_from_end_at, and instead
      reflect the actual object returned when you make updates - which instead
      includes the end_at date
    - fixed description of extra_attempts to be more clear
    - The example response should now correctly show quiz_extensions and not
      quiz_submissions
    - updated the description of extra_time in quiz submissions api to correctly
      describe it in 'minutes' instead of 'seconds'

  - I have updated the behavior of the manually_locked attribute.
    - Sending 1, '1', true, or 'true' will result in the attribute being
      set to true. Every other value will set the value to false.

Change-Id: Id6071632a8eb9d01d61cf21287955fb5e44c2f3f
Reviewed-on: https://gerrit.instructure.com/35305
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Caleb Guanzon <cguanzon@instructure.com>
Reviewed-by: Josh Simpson <jsimpson@instructure.com>
Product-Review: Derek DeVries <ddevries@instructure.com>