Lesson Viewer: Update module progress

[jfdoming]

Summary

We want to update the lessons within the sidebar based on whether a user has completed them.

Goals

• When a user clicks "Continue," we want to update the backend to reflect that they've completed a lesson.

Designs

N/A

Implementation

There's already a callback for the "Continue" button (onLessonCompleted in ModuleViewer.tsx); you'll just need to replace the TODO with a mutation call to the backend, and make sure that everything works as you'd expect.