Move graduate_users script to cronjob

[rm03]

The graduate_users script, which deactivates memberships for users who graduated before the current year, was originally intended to be executed manually via the admin console. Since this task should occur automatically at the beginning of each year, it makes more sense to have the script as a cronjob.

[aviupadhyayula]

LGTM, thanks Rohan. Would love to see a unit test for this command.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 71.47%. Comparing base (9612017) to head (f963183).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master     #730      +/-   ##
==========================================
+ Coverage   71.37%   71.47%   +0.09%     
==========================================
  Files          31       31              
  Lines        6848     6847       -1     
==========================================
+ Hits         4888     4894       +6     
+ Misses       1960     1953       -7     

Flag	Coverage Δ
	71.47% <ø> (+0.09%)	⬆️

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