Make flag order deterministic for helm's --setFiles

[gsquared94]

No guaranteed order in iterating map.

Test failure: here

[codecov]

Codecov Report

Merging #4779 into master will decrease coverage by 0.00%.
The diff coverage is 90.90%.

@@            Coverage Diff             @@
##           master    #4779      +/-   ##
==========================================
- Coverage   73.84%   73.84%   -0.01%     
==========================================
  Files         347      347              
  Lines       13753    13751       -2     
==========================================
- Hits        10156    10154       -2     
  Misses       2965     2965              
  Partials      632      632              

Impacted Files	Coverage Δ
pkg/skaffold/deploy/helm.go	78.66% <90.90%> (-0.12%)	⬇️

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