[CDF-23684] Fix update kafka or mqtt source in hosted extractor.

[doctrino]

Description

Issue is that these source uses a {"setNull": True} instead of of {"set": {}} for clearing objects.

Checklist:

• Tests added/updated.
• Documentation updated. Documentation is generated from docstrings - these must be updated according to your change.
  If a new method has been added it should be referenced in cognite.rst in order to generate docs based on its docstring.
• Changelog updated in CHANGELOG.md.
• Version bumped. If triggering a new release is desired, bump the version number in _version.py and pyproject.toml per semantic versioning.

[erlendvollset]

isNull: true should be supported for all APIs according to the design guide. Let's try chasing the teams owning those services to support it before adding a public option to configure it.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 90.70%. Comparing base (73fe764) to head (3b91a62).
Report is 1 commits behind head on master.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #2096      +/-   ##
==========================================
+ Coverage   90.69%   90.70%   +0.01%     
==========================================
  Files         149      149              
  Lines       22880    22883       +3     
==========================================
+ Hits        20750    20756       +6     
+ Misses       2130     2127       -3     

Files with missing lines	Coverage Δ
cognite/client/_api_client.py	90.38% <100.00%> (+0.03%)	⬆️
cognite/client/_version.py	100.00% <100.00%> (ø)
cognite/client/data_classes/_base.py	92.99% <100.00%> (+0.01%)	⬆️
...ent/data_classes/hosted_extractors/destinations.py	96.92% <100.00%> (+3.07%)	⬆️
...e/client/data_classes/hosted_extractors/sources.py	90.18% <ø> (ø)

... and 2 files with indirect coverage changes