make initContainer in localDir type of kaniko build param

[venkatk-25]

This is to parameterize the InitContainer Image in LocalDir build of kaniko, so we can use custom one apart from busybox, especially useful in private clouds where public repos are not accessible

[codecov-io]

Codecov Report

Merging #1727 into master will decrease coverage by 0.02%.
The diff coverage is 16.66%.

@@            Coverage Diff             @@
##           master    #1727      +/-   ##
==========================================
- Coverage   46.93%   46.91%   -0.03%     
==========================================
  Files         126      126              
  Lines        6176     6182       +6     
==========================================
+ Hits         2899     2900       +1     
- Misses       2979     2984       +5     
  Partials      298      298

Impacted Files	Coverage Δ
pkg/skaffold/schema/defaults/defaults.go	37.66% <16.66%> (-0.86%)	⬇️

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