section_id parameter for outcome result rollup endpoint

fixes CNVS-10035

test plan
- create a course with more than one section and users in each
 section
- fetch outcome results using api, specifying a section_id
- ensure that only users from the specified section are returned
- fetch course aggregate results, specifying a section_id
- ensure that only the users' scores from the specified section
 are used in the resulting average
- try to fetch outcome results using the api, specifying a
 section_id for a section not in the course
- ensure that an error is returned
- fetch some outcomes using the api without the section_id param
- ensure that results for all users in the course are returned

Change-Id: I8581f50ec239824daaa0782c4ebca575e3b8e65a
Reviewed-on: https://gerrit.instructure.com/28205
Reviewed-by: Zach Pendleton <zachp@instructure.com>
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Matt Fairbourn <mfairbourn@instructure.com>
Product-Review: Joel Hough <joel@instructure.com>