e2e flow for High Density GameServers

[markmandel]

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 PR includes two things, such that I believe we can close the below
issue:

1. An e2e test to confirm that the described flow in https://agones.dev/site/docs/integration-patterns/high-density-gameservers/
   works as expected (it does 😄).
2. Add a section in the integration documentation to highlight the consistency models (i.e. things are not atomic operations, but
   eventually consistent), and that people need to keep this in mind.

Which issue(s) this PR fixes:

Closes #2408

Special notes for your reviewer:

N/A

[agones-bot]

Build Succeeded 👏

Build Id: 4dc28176-24a9-4bd4-94bc-ea2859dba383

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

• image: gcr.io/agones-images/agones-controller:1.22.0-9eea218
• image: gcr.io/agones-images/agones-ping:1.22.0-9eea218
• Linux C++ SDK (build): agonessdk-1.22.0-9eea218-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.22.0-9eea218.zip

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

• https://9eea218-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2516/head:pr_2516 && git checkout pr_2516
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.22.0-9eea218

[agones-bot]

Build Succeeded 👏

Build Id: aff054d9-fd2b-426d-88c4-9080a72545ec

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

• image: gcr.io/agones-images/agones-controller:1.22.0-cadfba4
• image: gcr.io/agones-images/agones-ping:1.22.0-cadfba4
• Linux C++ SDK (build): agonessdk-1.22.0-cadfba4-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.22.0-cadfba4.zip

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

• https://cadfba4-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/2516/head:pr_2516 && git checkout pr_2516
• helm install ./install/helm/agones --namespace agones-system --name agones --set agones.image.tag=1.22.0-cadfba4

[google-oss-prow]

[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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