Backfill LMSUser.lms_api_user_id from the assignment roster data

[marcospri]

For:

• Store API IDs alongside LTI ones for users and courses #6880

The LMSUser.lms_api_user_id now filled in #6878 is also vaiivialbe in assignments rosters in Canvas.

We'll read it from the roster info while fetching it to speed up the backfill.

Testing

• Clear the DB to force roster fetching:

truncate task_done, assignment_roster;

• Clear any IDs you might have in the DB

update lms_user set lms_api_user_id = null;

• Launch a LTI1.3 assignment:

https://hypothesis.instructure.com/courses/319/assignments/3308

• Schedule the roster fetching, make shell:

from lms.tasks.roster import schedule_fetching_rosters
schedule_fetching_rosters.delay()

• Check that some users have been backfilled:

select display_name, lms_api_user_id from lms_user where lms_api_user_id is not null;
     display_name      | lms_api_user_id
-----------------------+-----------------
 DISPLAY NAME TEACHER  | 36
 Leopoldd              | 85
 eng+coursecopystudent | 255