[backend/frontend] Fix malware analyses pagination error on submission date if null (#6054)

[SouadHadjiat]

Proposed changes

• use missing: 0 for dates fixes the issue with sorting
• set submitted to nullable in malware creation and edition
• add test

Related issues

• Malware analyses pagination error on submission date if null #6054

To reproduce the issue locally, you need to create more than 25 malware analyses with at least one without a submitted date. You can also export malware analyses from testing platform and import them on your local platform.

Checklist

• I consider the submitted work as finished
• I tested the code for its functionality
• I wrote test cases for the relevant uses case
• I added/update the relevant documentation (either on github or on notion)
• Where necessary I refactored code to improve the overall quality

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Comparison is base (62f3386) 65.94% compared to head (2bf9b53) 65.95%.
Report is 2 commits behind head on master.

Additional details and impacted files

@@           Coverage Diff           @@
##           master    #6058   +/-   ##
=======================================
  Coverage   65.94%   65.95%           
=======================================
  Files         541      541           
  Lines       64286    64290    +4     
  Branches     5199     5201    +2     
=======================================
+ Hits        42395    42404    +9     
+ Misses      21891    21886    -5     

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