Canvas Optional Sections

## The Problem

There are a number of existing issues and support tickets derived from the confusion around Canvas Sections, which makes it impossible to access the course-level group, or any annotations therein. This can disrupt classes and lower adoption by pilot teachers especially. Customers can’t upgrade their Canvas app mid-semester because they lose access to old annotations upon upgrade. Some Canvas institutions have expressed that this is a problem with their student data retention policies.

## Scenario to enable

When Canvas admins upgrade to Sections groups the annotations in current and old courses should still be visible to users. Rather than defaulting sections **off** and effectively hiding the feature, we allow instances to turn **on** the feature, but then let teachers decide what grouping configuration they want.

## Related tickets

[Source of truth](https://github.com/orgs/hypothesis/projects/51/views/21?filterQuery=-status%3ADone+-is%3Aclosed+-type%3AFeature+feature%3A%22Canvas+Optional+Sections%22)

## References

https://hypothes-is.slack.com/archives/C2BLQDKHA/p1607709740356200