Release v1.21.0

[SaitejaTamma]

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

/Kind Release

What this PR does / Why we need it:

Which issue(s) this PR fixes:

Closes #2480

Special notes for your reviewer:

[agones-bot]

Build Succeeded 👏

Build Id: 51c5466f-9a04-4ef7-9641-05013e02771c

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

• image: gcr.io/agones-images/agones-controller:1.21.0-1ace087
• image: gcr.io/agones-images/agones-ping:1.21.0-1ace087
• Linux C++ SDK (build): agonessdk-1.21.0-1ace087-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.21.0-1ace087.zip

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

• https://1ace087-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2481/head:pr_2481 && git checkout pr_2481
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.21.0-1ace087

[google-oss-prow]

[APPROVALNOTIFIER] This PR is APPROVED

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

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• OWNERS [markmandel]

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[agones-bot]

Build Succeeded 👏

Build Id: 49c9add4-187b-4e24-9d8e-c47bc1f483bb

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

• image: gcr.io/agones-images/agones-controller:1.21.0-0c8b1af
• image: gcr.io/agones-images/agones-ping:1.21.0-0c8b1af
• Linux C++ SDK (build): agonessdk-1.21.0-0c8b1af-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.21.0-0c8b1af.zip

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

• https://0c8b1af-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2481/head:pr_2481 && git checkout pr_2481
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.21.0-0c8b1af