Set config creation time without mutating

[imjasonh]

This also sets layers' history creation times to the relevant times set in the tar files.

[codecov-commenter]

Codecov Report

Merging #524 (15b9ce1) into main (b813b95) will not change coverage.
The diff coverage is 100.00%.

@@           Coverage Diff           @@
##             main     #524   +/-   ##
=======================================
  Coverage   48.82%   48.82%           
=======================================
  Files          42       42           
  Lines        2204     2204           
=======================================
  Hits         1076     1076           
  Misses        946      946           
  Partials      182      182           

Impacted Files	Coverage Δ
pkg/build/gobuild.go	57.40% <100.00%> (+0.23%)	⬆️
pkg/commands/config.go	56.25% <0.00%> (-1.13%)	⬇️
pkg/commands/resolver.go	31.55% <0.00%> (-0.34%)	⬇️

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