Enabling Sections is a confusing experience for users and Canvas admins

**Describe the bug**
In LMS institutions where instructor enthusiasm helps us get an institutional deal, the process to enable Canvas Files and Sections at that institutions becomes complicated by the existing instructor installs of Hypothesis at the course level. These early adopters want their U to move to an install with a Developer Key so they can benefit from our Canvas Files and (potentially) Canvas Sections integrations.

One of Hypothesis' attractions for Canvas admins is the ease of the install and that we handle our own support; there are Canvas admins who might push back against Hypothesis or just not commit to doing an install with a Developer Key if they have to do additional work beyond a sub-account or account level install.

Having both these pieces in place helps Sales close new deals (even mid-semester) and will help Success retain deals in the future. Losing the ability for instructors to make course level installs on their own means we have less leverage for individual instructors to try us and then push their U to sign deals. Losing the ability to make this easy on an LMS admin means they might wait a semester to install with a Developer Key meaning we have less leverage to get folks to sign deals right now.

**To Reproduce**
What we've seen from partners with problems in this area
1. An early adopter instructor installs Hypothesis without a Dev Key in Canvas.
2. The university is convinced by the instructor's trial with Hypothesis and signs a deal with us.
3. The LMS admin creates an sub-account level install with a Developer Key
4. Either the instructor ends up with multiple installs or they are excluded from getting the benefits they pushed their University to get from us.

**Expected behavior**
An early adopter who installed with a course-level install should get at least some fo the benefits of the Canvas Dev Key (Canvas Files) and **possibly** all of the benefits (Canvas Sections on assignments going forward without losing access to the Canvas course group in previous assignments).

The LMS admin does the minimum amount of work (i.e., an account level install with a Dev Key with the instructor responsible for deleting their own course level install).

Start by clarifying the Canvas course-level and account-level installation behavior described in the reproduction steps, including the Developer Key, Canvas Files, and Canvas Sections requirements. Done should be defined as a course-level install receiving the intended benefits without duplicate installs, while keeping the LMS admin's work to an account-level install.

Written by the indexing model from the issue text.