Learner metrics endpoint - Prerelease for evaluation

[johnbaldwin]

This PR is for the initial evaluation version of the learner metrics endpoint for Matej's implementation on the front end and evaluation in production.

The endpoint is /figures/api/learner-metrics/

• There is a basic viewset just to exercise the code. The test requires test data to be filled out and tested in the response

• UserFilterSet needs to be updated or an alternate filter set needs to be used in order to provide more filtering, in particular

  • Show only users who have enrollments
  • Show only users who do not have enrollments
  • Show only users who have completed
  • Show only users who have not completed

• List serializers need to be added to prefetch data to improve API performance

• test_learner_metrics_viewset needs to be completed

• Updated the CourseEnrollment mock to provide the is_enrolled method

[johnbaldwin]

I need to fix the unit test. It is failing because it is getting all users instead of the expected users. Should still work in devsite. I'll work on that tomorrow

[codecov-commenter]

Codecov Report

Merging #239 into master will increase coverage by 0.15%. The diff coverage is 98.03%.

@@            Coverage Diff             @@
##           master     #239      +/-   ##
==========================================
+ Coverage   91.62%   91.78%   +0.15%     
==========================================
  Files          41       41              
  Lines        2078     2129      +51     
==========================================
+ Hits         1904     1954      +50     
- Misses        174      175       +1     

Impacted Files	Coverage Δ
figures/serializers.py	94.91% <97.22%> (+0.32%)	:arrow_up:
figures/urls.py	100.00% <100.00%> (ø)
figures/views.py	92.68% <100.00%> (+0.28%)	:arrow_up:

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