Add date filter to assignment progress CSV endpoints

[axlewin]

Adds an optional to_date URL parameter to the assignment progress CSV endpoints to allow question attempts to be filtered to only those occurring before a given date. The date must be provided as a Unix timestamp in ms, as is the case elsewhere.

[codecov]

Codecov Report

❌ Patch coverage is 25.92593% with 20 lines in your changes missing coverage. Please review.
✅ Project coverage is 40.37%. Comparing base (5abbb3d) to head (fedd788).
⚠️ Report is 44 commits behind head on main.

Files with missing lines	Patch %	Lines
...k/ac/cam/cl/dtg/isaac/quiz/PgQuestionAttempts.java	7.69%	10 Missing and 2 partials ⚠️
...a/uk/ac/cam/cl/dtg/isaac/api/AssignmentFacade.java	33.33%	4 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #787      +/-   ##
==========================================
+ Coverage   40.28%   40.37%   +0.08%     
==========================================
  Files         546      547       +1     
  Lines       23800    23740      -60     
  Branches     2906     2890      -16     
==========================================
- Hits         9588     9584       -4     
+ Misses      13311    13255      -56     
  Partials      901      901              

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