Update CRD API reference for Kubernetes 1.21.

[roberthbailey]

What type of PR is this?

Uncomment only one /kind <> line, press enter to put that in a new line, and remove leading whitespace from that line:

/kind breaking
/kind bug
/kind cleanup

/kind documentation

/kind feature
/kind hotfix

What this PR does / Why we need it: Manually edited crd-doc-config.json to point docs to the new k8s version. Then ran make gen-crd-client and make gen-api-docs.

Which issue(s) this PR fixes:

Work on #2311

Special notes for your reviewer:

[agones-bot]

Build Failed 😱

Build Id: fe41fc38-8699-450c-8234-a009c9b369e7

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• Cloud Build log download

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[agones-bot]

Build Failed 😱

Build Id: 0c02113d-83a8-435a-9a7b-42c2711ae865

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[agones-bot]

Build Succeeded 👏

Build Id: 1241754a-c22e-4711-849f-1d50a06091f2

The following development artifacts have been built, and will exist for the next 30 days:

• image: gcr.io/agones-images/agones-controller:1.19.0-10db8bb
• image: gcr.io/agones-images/agones-ping:1.19.0-10db8bb
• Linux C++ SDK (build): agonessdk-1.19.0-10db8bb-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.19.0-10db8bb.zip

A preview of the website (the last 30 builds are retained):

• https://10db8bb-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2334/head:pr_2334 && git checkout pr_2334
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.19.0-10db8bb

[google-oss-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: markmandel, roberthbailey

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• OWNERS [markmandel,roberthbailey]

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