Fix raw extension openapi definition

[jennybuckley]

What type of PR is this?
/kind bug
/sig api-machinery
/priority important-longterm

What this PR does / why we need it:
Changes the definition of RawExtension to this (adding json:"-")

type RawExtension struct {
    ...
    Raw []byte `json:"-" protobuf:"bytes,1,opt,name=raw"`
    ...
}

I noticed that this removes Raw from the openapi defintion of it, making it just type: object, without changing how it is marshalled or unmarshalled (since we have custom functions for that). This fixes a known issue with the client side validation of RawExtension

Which issue(s) this PR fixes:
Fixes #55890

Does this PR introduce a user-facing change?:

Fixed a bug with the openAPI definition for io.k8s.apimachinery.pkg.runtime.RawExtension, which previously required a field "raw" to be specified

[jennybuckley]

/retest

[jennybuckley]

/assign @roycaihw

[jennybuckley]

/retest

[jennybuckley]

/retest

[jennybuckley]

/retest

[roycaihw]

/lgtm

This doesn't introduce any user-facing change in apiserver handling a request (besides the openapi spec itself is visible to user), but it will cause a few client-side change that are user-facing (kubectl and the openapi-generated clients won't require raw in a field of RawExtension type and/or error on unknown fields). Could you add a release note mentioning that the spec is fixed?

also please squash the first and the third commits

[jennybuckley]

/retest
@roycaihw I think this is ready now

[lavalamp]

nice find

/approve

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: jennybuckley, lavalamp

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• api/OWNERS [lavalamp]
• staging/src/k8s.io/apiextensions-apiserver/OWNERS [lavalamp]
• staging/src/k8s.io/apimachinery/pkg/OWNERS [lavalamp]
• staging/src/k8s.io/code-generator/OWNERS [lavalamp]
• staging/src/k8s.io/sample-apiserver/OWNERS [lavalamp]

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[roycaihw]

/lgtm