expose v1/layout.WriteImage and WriteIndex

[deitch]

Fixes #813

[jonjohnsonjr]

@mattmoor @imjasonh this CodeQL things sucks, I often do want to log credentials for debugging reasons.

[mattmoor]

Logging credentials is a huge security problem, logs are often far more accessible than the credentials potentially logged to them. This has resulted in a large number of security incidents.

[codecov-io]

Codecov Report

Merging #815 into master will not change coverage.
The diff coverage is 0.00%.

@@           Coverage Diff           @@
##           master     #815   +/-   ##
=======================================
  Coverage   74.77%   74.77%           
=======================================
  Files         103      103           
  Lines        4313     4313           
=======================================
  Hits         3225     3225           
  Misses        611      611           
  Partials      477      477           

Impacted Files	Coverage Δ
pkg/v1/layout/write.go	48.41% <0.00%> (ø)

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[jonjohnsonjr]

Thanks!