Enforce one platform policy for GardenLinux canonical names and enhance S3 artifact handling

[NotTheEvilOne]

What this PR does / why we need it:
This PR changes the GardenLinux canonical name behavior and features parser to only accept one platform. It further enhances S3 artifact handling to respect more values of *.release files.

Which issue(s) this PR fixes:
Related gardenlinux/gardenlinux#3816
Supersedes #249
Fixes gardenlinux/gardenlinux#3824
Fixes #244

[codecov]

Codecov Report

❌ Patch coverage is 76.82927% with 19 lines in your changes missing coverage. Please review.
✅ Project coverage is 91.20%. Comparing base (d64300c) to head (15aa2a7).
⚠️ Report is 18 commits behind head on main.

Files with missing lines	Patch %	Lines
src/gardenlinux/features/__main__.py	61.29%	12 Missing ⚠️
src/gardenlinux/features/cname.py	62.50%	6 Missing ⚠️
src/gardenlinux/s3/s3_artifacts.py	85.71%	1 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #248      +/-   ##
==========================================
+ Coverage   90.63%   91.20%   +0.56%     
==========================================
  Files          42       42              
  Lines        2008     2024      +16     
==========================================
+ Hits         1820     1846      +26     
+ Misses        188      178      -10     

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