FR-6315 - Support generating Deb822 sources list

[upils]

Add support for generating deb822 sources list files when building an image.

This feature is enabled via a new field in the Rootfs object of the image definition.

If the user does not explicitly set this value to "true", a warning is displayed explaining this will be the default value at some point in the future.

Once this is merged, we should update our image definitions.

[codecov]

Codecov Report

Attention: Patch coverage is 63.70370% with 49 lines in your changes are missing coverage. Please review.

Project coverage is 89.25%. Comparing base (950c773) to head (818be56).

Files	Patch %	Lines
internal/imagedefinition/image_definition.go	54.44%	41 Missing ⚠️
internal/statemachine/classic_states.go	78.37%	5 Missing and 3 partials ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #186      +/-   ##
==========================================
- Coverage   89.88%   89.25%   -0.64%     
==========================================
  Files          13       13              
  Lines        3531     3630      +99     
==========================================
+ Hits         3174     3240      +66     
- Misses        319      350      +31     
- Partials       38       40       +2     

Flag	Coverage Δ
unittests	89.25% <63.70%> (-0.64%)	⬇️

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[sil2100]

This LGTM! One inline indentation comment and a question about the extent of the deb822 migration we're doing in noble. But otherwise, this is good to go.

[julian-klode]

Generally approving this but as commented, the warning could use some rewording

[sil2100]

With Julian's comments, I'm now +1 on it. The wording seems to be fine for me as well. Please proceed!