Preparation for Release v1.51.0

[0xaravindh]

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 #4206

Special notes for your reviewer:

[agones-bot]

Build Failed 😭

Build Id: 609a3b51-ac98-4593-929d-8242b0c49d7a

Status: FAILURE

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[0xaravindh]

Getting error in "gke-autopilot-upgrade-test-cluster-1-33"

**cilium-agent-metrics-collector… {"caller":"gcm/export.go:505", "error":"rpc error: code = InvalidArgument desc = One or more TimeSeries could not be written: timeSeries[8] (metric.type="kubernetes.io/internal/node_token_broker_status", 
metric.labels={"status": "GOT_COMPUTE_TOKEN", "mode": "MODE_COMPUTE_ENGINE_TOKEN"}): write for resource=k8s_container{cluster_name:gke-autopilot-upgrade-test-cluster-1-33,namespace_name:kube-system,location:us-central1,pod_name:anetd-l-5dl5z,container_name:cilium-agent-metrics-collector} 
failed with: One or more points were written more frequently than the maximum sampling period configured for the metric. {Metric: kubernetes.io/internal/node_token_broker_status, Timestamps: {Youngest Existing: '2025/06/18-11:57:35.154', New: 
'2025/06/18-11:57:35.154'}}", "level":"error", "msg":"Failed to export self-observability metrics to Cloud Monitoring", "stacktrace":"google3/cloud/kubernetes/metrics/common/gcm/gcm.(*exporter).startSelfObservability cloud/kubernetes/metrics/common/gcm/export.go:505", "ts":1.7502730551978583E9}**

[0xaravindh]

/gcbrun

[agones-bot]

Build Failed 😭

Build Id: 4cde9cd0-80f7-4092-96bc-c3b4fc689f91

Status: FAILURE

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[igooch]

/gcbrun

[agones-bot]

Build Succeeded 🥳

Build Id: 3f6c6aad-160a-4ca1-82b7-480ef889781a

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:1.51.0-dev-986e0dc
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.51.0-dev-986e0dc
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.51.0-dev-986e0dc-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.51.0-dev-986e0dc
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.51.0-dev-986e0dc
• Linux C++ SDK (build): agonessdk-1.51.0-dev-986e0dc-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.51.0-dev-986e0dc.zip

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

• https://986e0dc-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4209/head:pr_4209 && git checkout pr_4209
helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.51.0-dev-986e0dc