[#1050] Implemented basic zaakinformationobject notifications

[Bartvaderkin]

The diff/changes look worse then it is:

• I had to rearrange the checks in the first part of the handler (and its tests) as they are the same for both notifications.
• I also subdivided the notification test files in an attempt to keep file size and code volume manageable, so a lot of what seems new is actually old.

[codecov-commenter]

Codecov Report

Merging #459 (7c10355) into develop (73137fd) will increase coverage by 0.02%.
The diff coverage is 97.98%.

@@             Coverage Diff             @@
##           develop     #459      +/-   ##
===========================================
+ Coverage    96.43%   96.45%   +0.02%     
===========================================
  Files          495      502       +7     
  Lines        17664    18068     +404     
===========================================
+ Hits         17034    17428     +394     
- Misses         630      640      +10     

Impacted Files	Coverage Δ
src/open_inwoner/conf/base.py	95.06% <ø> (ø)
src/open_inwoner/openzaak/documents.py	94.59% <ø> (-0.08%)	⬇️
src/open_inwoner/openzaak/cases.py	78.53% <80.00%> (+<0.01%)	⬆️
src/open_inwoner/openzaak/admin.py	90.35% <89.65%> (-0.35%)	⬇️
src/open_inwoner/openzaak/tests/factories.py	98.57% <90.00%> (-1.43%)	⬇️
src/open_inwoner/openzaak/models.py	97.82% <90.90%> (-2.18%)	⬇️
src/open_inwoner/openzaak/notifications.py	95.12% <96.00%> (-0.34%)	⬇️
src/open_inwoner/openzaak/managers.py	96.07% <96.55%> (+9.41%)	⬆️
...n_inwoner/openzaak/tests/test_notification_data.py	98.21% <98.21%> (ø)
...ner/openzaak/migrations/0011_auto_20230207_1030.py	100.00% <100.00%> (ø)
... and 13 more

📣 We’re building smart automated test selection to slash your CI/CD build times. Learn more

[vaszig]

It looks good to me, I would like to test it together tomorrow.