show approximate number of students who have learned on code.org - #47752

As part of Milestone 1 of Separating Pegasus, we need to eliminate places where dashboard code accesses pegasus DB.

The purpose of this PR is to remove the following pegasus DB accesses from dashboard:

• code-dot-org/dashboard/app/views/courses/index.html.haml

  Line 2 in a23aa45

  lines_count = fetch_metrics['lines_of_code']

• code-dot-org/dashboard/app/views/courses/index.html.haml

  Line 4 in a23aa45

  students_count = fetch_user_metrics['number_students']

See screenshots below for user-visible changes on https://studio.code.org/courses as a result of hard-coding the number of students. The marketing team has agreed to these changes (see slack), and will own asking for this number to be updated whenever the number of students reaches the next multiple of 10M.

Also, there is no visible change associated with removing the fetch for lines_of_code, presumably because it was removed from the UI in a previous PR.

Screenshots

student

signed out

teacher

The teacher view for /courses is unchanged:

Testing story

• existing UI test coverage verifies that the courses page still loads for teachers, students and signed-out users.

Deployment strategy

normally we have to be careful about deploying translatable string changes, however in this case the new string text seems backward compatible enough, i.e. it seems ok that it will say "70M students learned" instead of "Over 70M..." or "73M students learned" for a short period of time. so I am just planning to merge the string change and the code change as part of the same PR, rather than creating a whole separate string and then waiting for it to be translated.

Follow-up work

ideally this would not need to be updated manually in the future. the work to figure out how to share this kind of data between dashboard and pegasus will be tracked as part of the ongoing effort to separate pegasus from dashboard.