Add optional fields into build and copy to backend

[colerogers]

Fixes #4744

[codecov-commenter]

Codecov Report

Merging #4746 (d91d37b) into master (4992be4) will increase coverage by 0.02%.
The diff coverage is 100.00%.

@@            Coverage Diff             @@
##           master    #4746      +/-   ##
==========================================
+ Coverage   57.57%   57.59%   +0.02%     
==========================================
  Files         287      287              
  Lines       18511    18518       +7     
  Branches     3620     3622       +2     
==========================================
+ Hits        10658    10666       +8     
+ Misses       6979     6978       -1     
  Partials      874      874              

Impacted Files	Coverage Δ
src/deploy/functions/build.ts	74.59% <100.00%> (+1.54%)	⬆️
...rc/deploy/functions/runtimes/discovery/v1alpha1.ts	79.88% <0.00%> (+0.55%)	⬆️

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[Berlioz]

LGTM