Exclude CRD schema from transformation, fix #1737.

[mgoltzsche]

Fixes #1737.

Description

Replaces the fuzzy Replacer/Matcher interfaces with a simple FieldVisitor interface.
In case the provided manifest is not a CustomResourceDefinition the provided visitor is decorated to perform recursion.

My issue comment here provides some background information.

Using this approach other transformation rules could be implemented as decorators of FieldVisitor objects as well.

cc @tejal29

User facing changes

Users will be able to deploy CRDs using skaffold.

Before

CRD deployment failed since skaffold added labels to the metadata specification within the CRD's OpenAPI schema which should actually remain untouched.

After

CRD fields other than in the first level are not traversed. Therefore CRD schemas remain untouched while the CRD is still labeled.

Submitter Checklist

• Includes unit tests
• Mentions any output changes.
• Adds documentation as needed: user docs, YAML reference, CLI reference - none needed
• Adds integration tests if needed - none needed

Reviewer Notes

• The code flow looks good.
• Unit test added.
• User facing changes look good.

Release Notes

- CRD support: exclude schema from transformation

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[mgoltzsche]

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[codecov]

Codecov Report

Merging #3456 into master will increase coverage by 0.08%.
The diff coverage is 100%.

Impacted Files	Coverage Δ
pkg/skaffold/deploy/kubectl/labels.go	92.85% <100%> (+14.28%)	⬆️
pkg/skaffold/deploy/kubectl/namespaces.go	90.9% <100%> (+8.3%)	⬆️
pkg/skaffold/deploy/kubectl/images.go	100% <100%> (+7.27%)	⬆️
pkg/skaffold/deploy/kubectl/visitor.go	93.54% <100%> (-0.21%)	⬇️
...affold/kubernetes/portforward/kubectl_forwarder.go	65.85% <0%> (-2.44%)	⬇️
pkg/skaffold/util/tar.go	57.47% <0%> (+4.59%)	⬆️

[dgageot]

LGTM. I'd like to wait for @tejal29's review

[nkubala]

nice!