refactor(compiler): move script gen outside of compiler and into container

[ecrupper]

By moving this routine outside of the compiler and into the pipeline.Container method set, we can call it in the worker code. This fixes the issue introduced in #1353 where if a user has ${VELA_BUILD_NUMBER} or ${VELA_BUILD_LINK} in their commands block, it would need to be declared in a way that allows shell substitution.

While this is probably not all that common (and fixable), I would argue this script routine is better suited as a container method anyway. It does not rely on any compiler information.

[codecov]

Codecov Report

❌ Patch coverage is 93.10345% with 2 lines in your changes missing coverage. Please review.
✅ Project coverage is 58.25%. Comparing base (3ebd7d0) to head (e2f2d26).
⚠️ Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
compiler/types/pipeline/container.go	93.10%	1 Missing and 1 partial ⚠️

❌ Your project status has failed because the head coverage (58.25%) is below the target coverage (90.00%). You can increase the head coverage or adjust the target coverage.

Additional details and impacted files

@@            Coverage Diff             @@
##             main    #1403      +/-   ##
==========================================
- Coverage   58.26%   58.25%   -0.01%     
==========================================
  Files         661      660       -1     
  Lines       25301    25286      -15     
==========================================
- Hits        14742    14731      -11     
+ Misses       9870     9868       -2     
+ Partials      689      687       -2     

Files with missing lines	Coverage Δ
compiler/native/compile.go	74.25% <ø> (+0.72%)	⬆️
compiler/types/pipeline/container.go	84.61% <93.10%> (+1.93%)	⬆️

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