Add a method to extract files from a docker image last layer

[Itxaka]

Part of kairos-io/kairos#2631

[codecov]

Codecov Report

Attention: Patch coverage is 65.38462% with 18 lines in your changes missing coverage. Please review.

Project coverage is 52.01%. Comparing base (dc46baf) to head (0384b9a).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
sysext/sysext.go	65.38%	14 Missing and 4 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #362      +/-   ##
==========================================
+ Coverage   51.33%   52.01%   +0.68%     
==========================================
  Files          17       18       +1     
  Lines        1315     1367      +52     
==========================================
+ Hits          675      711      +36     
- Misses        531      544      +13     
- Partials      109      112       +3     

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[Itxaka]

@mudler will this cover this kairos-io/kairos#2631 ?

Still needs work but it currently does what was expected. we should probably expand with tickets on creation of sysexts and such and we need to discuss where to put the command to create those sysexts/confexts as this is only a helper