Add LoadKernelExtension

[limakzi]

Solves gap-system/gap#5761.

The build failed because of codecov; everyone around agrees to ignore testing such thing.

[codecov]

Codecov Report

Attention: Patch coverage is 66.66667% with 1 line in your changes missing coverage. Please review.

Project coverage is 95.71%. Comparing base (1e63995) to head (0ab4d72).
Report is 1 commits behind head on master.

Files	Patch %	Lines
init.g	50.00%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master      #33      +/-   ##
==========================================
- Coverage   96.47%   95.71%   -0.77%     
==========================================
  Files           6        6              
  Lines         142      140       -2     
==========================================
- Hits          137      134       -3     
- Misses          5        6       +1     

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