validate: Expose hooks to inject custom behavior during traversal

[alexzielenski]

Adds a new Option to the schema validator for users to provider custom constructors for subfield and subindex-validators created during traversal.

/cc @stts @apelisse @jpbetz

[k8s-ci-robot]

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In response to this:

Proof of concept that adds a ratcheting validator to kube-openapi. Taking care to change code as minimally as possible.

More complicated/expansive tests forthcoming.

Ignores allOf, anyOf, not, oneOf for the purposes of ratcheting.

Still need to evaluate proper handling of required/dependentProperties and other cases which may not be caught by current DeepEqual.

/cc @stts @apelisse @jpbetz

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[alexzielenski]

/cc @sttts

[apelisse]

Looks good to me, Stefan, can you tag it?
/approve

[jpbetz]

/approve

I'll defer to @sttts for lgtm

[sttts]

Lgtm with exception of https://github.com/kubernetes/kube-openapi/pull/406/files#r1263940329.

[alexzielenski]

removed string slice logic

[alexzielenski]

/label tide/merge-method-squash

[sttts]

/lgtm
/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alexzielenski, apelisse, jpbetz, sttts

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