builder: Enable Command Substitution for RetryPolicy configuration

[yohamta]

• Enabled command substitution and environment variables for retry policy configuration

[codecov]

Codecov Report

Attention: Patch coverage is 33.92857% with 37 lines in your changes missing coverage. Please review.

Project coverage is 58.57%. Comparing base (3093ae2) to head (d622e4f).
Report is 1 commits behind head on main.

Files with missing lines	Patch %	Lines
internal/digraph/scheduler/node.go	42.30%	12 Missing and 3 partials ⚠️
internal/cmdutil/cmdutil.go	0.00%	14 Missing ⚠️
internal/digraph/builder.go	42.85%	8 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main     #747      +/-   ##
==========================================
- Coverage   58.87%   58.57%   -0.31%     
==========================================
  Files          68       68              
  Lines        6560     6609      +49     
==========================================
+ Hits         3862     3871       +9     
- Misses       2394     2430      +36     
- Partials      304      308       +4     

Files with missing lines	Coverage Δ
internal/digraph/scheduler/scheduler.go	83.28% <100.00%> (ø)
internal/digraph/step.go	100.00% <ø> (ø)
internal/digraph/builder.go	72.95% <42.85%> (-1.46%)	⬇️
internal/cmdutil/cmdutil.go	67.72% <0.00%> (-5.42%)	⬇️
internal/digraph/scheduler/node.go	76.33% <42.30%> (-2.69%)	⬇️

... and 1 file with indirect coverage changes

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