Feature: Added support for OpenAPI validations marker comments

[Schnides123]

This PR adds the ability to annotate API fields with basic OpenAPI schema validations via marker comments, as part of the KEP-4153: Declarative Validation feature.

/assign @alexzielenski

[linux-foundation-easycla[bot]]

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• :white_check_mark: login: Schnides123 / name: Alex Schneider (a06b51725f5ca21c9616251b95f9808ad69e9752)

[k8s-ci-robot]

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[alexzielenski]

/ok-to-test

[k8s-ci-robot]

@alexzielenski: GitHub didn't allow me to request PR reviews from the following users: WDYT, is, preferable.

Note that only kubernetes members and repo collaborators can review this PR, and authors cannot review their own PRs.

In response to [this](https://github.com/kubernetes/kube-openapi/pull/435#discussion_r1361227273): >An alternative to using these helper functions is to do as you did in the test by abusing the array literal notation: > >``` >&[]float64{20.0}[0] >``` > >/cc @apelisse WDYT is preferable Instructions for interacting with me using PR comments are available [here](https://git.k8s.io/community/contributors/guide/pull-requests.md). If you have questions or suggestions related to my behavior, please file an issue against the [kubernetes/test-infra](https://github.com/kubernetes/test-infra/issues/new?title=Prow%20issue:) repository.

[apelisse]

I would still add an intergration test. Create a new directory for value validation in https://github.com/kubernetes/kube-openapi/tree/master/test/integration/testdata, add some types in there with various validation markers, carefully follow the README including the notes at the bottom. Thanks!

[Schnides123]

I have been told to add the prefix back in, so the prefix is now back in

[alexzielenski]

/label tide/merge-method-squash /lgtm

[alexzielenski]

/hold

can you squash (tide concats the descriptions which is not useful)

edit: i squashed for you

[alexzielenski]

/ok-to-test

[alexzielenski]

/hold cancel /lgtm

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: alexzielenski, Schnides123

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/kubernetes/kube-openapi/blob/master/OWNERS)~~ [alexzielenski] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment