User can view dropoff in problem engagement by section and subsection for learner group

[crathbun428]

User Story
As a course author, I want to be able to see how many learners in my learner group attempted the problems in each section and subsection of my course, so that I have an easy way to view where the majority of my learners in my learner group stop engaging with my course content.

Acceptance Criteria
Scenario: A course author can see the dropoff in problem engagement by section and subsection for my learner group
Given I am a course author with X permissions
When I view the view dropoff visualization in the course engagement section of the learner group reports
Then I see the number of learners in my learner group who attempted at least one problem for each section/subsection of my course
And I see the number of learners in my learner group who attempted all problems for each section/subsection of my course