✨ - feat: store zaak selection on server

[svenvandescheur]

Research for #84 / Jira PZ-1721.

First step is to have the existing zaak selection moved from session storage to an API. in the future we should be able to pull changes from the API and apply them to our selection. This could allow for near-real time collaboration.

[codecov-commenter]

Codecov Report

Attention: Patch coverage is 77.41935% with 21 lines in your changes missing coverage. Please review.

Project coverage is 91.28%. Comparing base (cfc0aaa) to head (8c2bdc8).

Files	Patch %	Lines
...nd/src/openarchiefbeheer/selection/api/viewsets.py	53.65%	19 Missing ⚠️
backend/src/openarchiefbeheer/selection/models.py	87.50%	2 Missing ⚠️

Additional details and impacted files

@@             Coverage Diff             @@
##             main     #191       +/-   ##
===========================================
+ Coverage   77.02%   91.28%   +14.26%     
===========================================
  Files         191      136       -55     
  Lines        5602     4740      -862     
  Branches      101        0      -101     
===========================================
+ Hits         4315     4327       +12     
+ Misses       1188      413      -775     
+ Partials       99        0       -99     

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