Clarify docs on GKE Autopilot and node pools

[danfairs]

What this PR does / Why we need it:

/kind documentation

Which issue(s) this PR fixes:

This change makes it clearer that the cluster administrator does not need to manually configure
node pools when using GKE Autopilot.

[markmandel]

/gcbrun so we can get a preview.

[agones-bot]

Build Succeeded 🥳

Build Id: 32cb945c-e2d6-411e-ba86-f5ec5a2d12d5

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:1.46.0-dev-1bb03b7
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.46.0-dev-1bb03b7
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.46.0-dev-1bb03b7-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.46.0-dev-1bb03b7
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.46.0-dev-1bb03b7
• Linux C++ SDK (build): agonessdk-1.46.0-dev-1bb03b7-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.46.0-dev-1bb03b7.zip

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

• https://1bb03b7-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4048/head:pr_4048 && git checkout pr_4048
helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.46.0-dev-1bb03b7

[igooch]

LGTM