update API doc required params - 5

- Discussion topics
- Enrollment terms
- Enrollments
- External tools
- Favorites

Test plan:
- rake doc:api
- Verify the above doc pages for parameters accuracy

Refs SIS-403

Change-Id: I5a926cf36f0852c11356719f76b5b54bd25f96da
Reviewed-on: https://gerrit.instructure.com/38805
Tested-by: Jenkins <jenkins@instructure.com>
Reviewed-by: Tyler Pickett <tpickett+gerrit@instructure.com>
Product-Review: Tyler Pickett <tpickett+gerrit@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>