Update parameters in the following API docs
- Content migrations
- Conversations
- Course audit log
- Courses
- Custom gradebook columns

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

Change-Id: I4802bfcec067098658b573f54049b1f929f38ebc
Reviewed-on: https://gerrit.instructure.com/38691
Tested-by: Jenkins <jenkins@instructure.com>
QA-Review: Jeremy Putnam <jeremyp@instructure.com>
Reviewed-by: Tyler Pickett <tpickett+gerrit@instructure.com>
Product-Review: Tyler Pickett <tpickett+gerrit@instructure.com>