update API doc required params - 6

- Feature flags
- Files
- Grade change log
- Gradebook history
- Grading standards

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

Refs SIS-403

Change-Id: I52627a9bd557682c12713455e989d2e054c744b6
Reviewed-on: https://gerrit.instructure.com/38808
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>