feat: add extra command line support for boot entries

[Itxaka]

Include additional command lines in the boot entry configuration to enhance flexibility during the boot process. Also, update Dockerfile to install llvm for uki building.

[codecov]

Codecov Report

❌ Patch coverage is 0% with 59 lines in your changes missing coverage. Please review.
✅ Project coverage is 29.90%. Comparing base (e5697c6) to head (b2a4975).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/cmd/build-uki.go	0.00%	59 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #373      +/-   ##
==========================================
- Coverage   30.21%   29.90%   -0.32%     
==========================================
  Files          25       25              
  Lines        3902     3943      +41     
==========================================
  Hits         1179     1179              
- Misses       2535     2576      +41     
  Partials      188      188              

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