feat: add support for Kaniko flag --cache-copy-layers

[callahanca]

Related: #6380 references adding this flag and was used as a reference for this PR.

Description

Add Kaniko's "--cache-copy-layers" flag (https://github.com/GoogleContainerTools/kaniko#--cache-copy-layers), which tells Kaniko to cache COPY layers.

User facing changes

New option cacheCopyLayers in kaniko section

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[callahanca]

@googlebot I signed it!

[tejal29]

@callahanca Thank you for your PR. Please hold off until the #6702 goes in.

[tejal29]

@callahanca Can you please refer to the steps here to add new config to already released config.

[tejal29]

Thanks @callahanca. Will review once #6730 is in

[callahanca]

Thanks @tejal29! I also went ahead and rebased off of main.

[codecov]

Codecov Report

Merging #6703 (a9df811) into main (290280e) will decrease coverage by 0.84%.
The diff coverage is 50.00%.

@@            Coverage Diff             @@
##             main    #6703      +/-   ##
==========================================
- Coverage   70.48%   69.63%   -0.85%     
==========================================
  Files         515      527      +12     
  Lines       23150    24093     +943     
==========================================
+ Hits        16317    16778     +461     
- Misses       5776     6212     +436     
- Partials     1057     1103      +46     

Impacted Files	Coverage Δ
cmd/skaffold/app/cmd/flags.go	89.00% <0.00%> (-1.82%)	⬇️
cmd/skaffold/skaffold.go	0.00% <ø> (ø)
cmd/skaffold/app/cmd/cmd.go	70.32% <66.66%> (-0.73%)	⬇️
cmd/skaffold/app/cmd/debug.go	100.00% <100.00%> (ø)
pkg/skaffold/initializer/build/builders.go	42.85% <0.00%> (-17.15%)	⬇️
pkg/skaffold/build/cluster/logs.go	0.00% <0.00%> (-16.67%)	⬇️
pkg/skaffold/event/v2/status_check.go	85.45% <0.00%> (-14.55%)	⬇️
pkg/skaffold/kubernetes/watcher.go	67.10% <0.00%> (-14.53%)	⬇️
pkg/skaffold/log/stream/stream.go	71.42% <0.00%> (-14.29%)	⬇️
.../skaffold/kubernetes/status/resource/deployment.go	72.41% <0.00%> (-13.39%)	⬇️
... and 92 more

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[tejal29]

Thanks!

[callahanca]

Hm, I guess this is blocked by the kokoro build failure. I didn't really see the specific error in the kaniko_microservices test; is that a test that I can run myself locally?

[MarlonGamez]

hey @callahanca, we were having some issues with our kaniko tests but they've been resolved now. I'll put kokoro to run again for you PR