Add allocator readiness configurations doc

[chiayi]

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:
This adds the documentation for the helm configurations used by allocator

Which issue(s) this PR fixes:
Follow up for #3105

Special notes for your reviewer:

[agones-bot]

Build Failed 😱

Build Id: 84c70039-8216-41fa-9a02-da1fc79aa716

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[agones-bot]

Build Failed 😱

Build Id: 025f42bf-9176-40a8-9fba-4fe495706031

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[agones-bot]

Build Failed 😱

Build Id: 6dc4cec6-3b22-458c-91de-a9433342829c

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[agones-bot]

Build Succeeded 👏

Build Id: 49581667-0da6-4bb1-9a82-534e8e6c1a59

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

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.32.0-a930bcc-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.32.0-a930bcc-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.32.0-a930bcc-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.32.0-a930bcc-amd64
• Linux C++ SDK (build): agonessdk-1.32.0-a930bcc-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.32.0-a930bcc-amd64.zip

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

• https://a930bcc-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3142/head:pr_3142 && git checkout pr_3142
• helm install agones ./install/helm/agones --namespace agones-system --agones.image.release=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.32.0-a930bcc-amd64

[agones-bot]

Build Failed 😱

Build Id: 6aadcb3b-6717-471e-aa81-49c76b33fefc

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[agones-bot]

Build Failed 😱

Build Id: a11be064-8653-4059-8be1-16bb31c92bf5

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• Cloud Build log download

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[agones-bot]

Build Succeeded 👏

Build Id: f424f65d-d9d0-4d6a-9872-e2d2a445ae39

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

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.32.0-ea5be28-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.32.0-ea5be28-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.32.0-ea5be28-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.32.0-ea5be28-amd64
• Linux C++ SDK (build): agonessdk-1.32.0-ea5be28-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.32.0-ea5be28-amd64.zip

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

• https://ea5be28-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3142/head:pr_3142 && git checkout pr_3142
• helm install agones ./install/helm/agones --namespace agones-system --agones.image.release=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.32.0-ea5be28-amd64

[agones-bot]

Build Succeeded 👏

Build Id: 204ef6e2-a16c-4d7c-9bab-04d35020b1c4

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

• image: us-docker.pkg.dev/agones-images/ci/agones-controller:1.32.0-ea5be28-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.32.0-ea5be28-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.32.0-ea5be28-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.32.0-ea5be28-amd64
• Linux C++ SDK (build): agonessdk-1.32.0-ea5be28-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.32.0-ea5be28-amd64.zip

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

• https://ea5be28-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3142/head:pr_3142 && git checkout pr_3142
• helm install agones ./install/helm/agones --namespace agones-system --agones.image.release=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.32.0-ea5be28-amd64

[google-oss-prow]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: chiayi, zmerlynn
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