apiextensions: promote CustomResourcesSubresources to beta

[nikhita]

Fixes #62786

This PR promotes the CustomResourcesSubResources feature to beta and makes it enabled by default.

Release note:

Subresources for custom resources is now beta and enabled by default. With this, updates to the `/status` subresource will disallow updates to all fields other than `.status` (not just `.spec` and `.metadata` as before). Also, `required` can be used at the root of the CRD OpenAPI validation schema when the `/status` subresource is enabled.

/assign sttts deads2k
/sig api-machinery
/area custom-resources

[sttts]

Staging godeps must be updated.

[sttts]

/assign @liggitt

for approval of api and feature changes.

[nikhita]

Staging godeps must be updated.

Done.

[ncdc]

/uncc

[nikhita]

/retest

[lavalamp]

/assign @mbohlool

[nikhita]

/retest

[nikhita]

All tests are green.

[sttts]

/lgtm
/approve

[nikhita]

@liggitt approved?

[nikhita]

/uncc dchen1107

[sttts]

@liggitt ping

[liggitt]

/lgtm
/retest

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liggitt, nikhita, sttts

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Needs approval from an approver in each of these files:

• api/OWNERS [liggitt]
• pkg/features/OWNERS [liggitt]
• staging/src/k8s.io/apiextensions-apiserver/OWNERS [sttts]

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[k8s-github-robot]

/test all [submit-queue is verifying that this PR is safe to merge]

[k8s-ci-robot]

@nikhita: The following test failed, say /retest to rerun them all:

Test name	Commit	Details	Rerun command
pull-kubernetes-e2e-gce	0e32006	link	/test pull-kubernetes-e2e-gce

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[k8s-github-robot]

Automatic merge from submit-queue (batch tested with PRs 63598, 63913, 63459, 63963, 60464). If you want to cherry-pick this change to another branch, please follow the instructions here.