Bump simple-game-server references to 0.19

[zmerlynn]

I pushed simple-game-server:0.19 after #3436 was merged, update all references to verify it still works with everything.

Note to reviewers: This was simply:

for f in $(grep -lR simple-game-server:0.18); do
  sed -i "s/simple-game-server:0.18/simple-game-server:0.19/g" $f
done

I double checked this with grep -R simple-game-server | grep 0.18 after, which showed only the changelog.

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This pull-request has been approved by: gongmax, roberthbailey, zmerlynn

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Build Succeeded 👏

Build Id: 6f4b1e09-83a7-4286-979f-7b1290a3491d

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:1.36.0-dev-e660011-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.36.0-dev-e660011-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.36.0-dev-e660011-linux-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.36.0-dev-e660011-amd64
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.36.0-dev-e660011-amd64
• Linux C++ SDK (build): agonessdk-1.36.0-dev-e660011-amd64-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.36.0-dev-e660011-amd64.zip

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

• https://e660011-dot-preview-dot-agones-images.appspot.com/

To install this version:

• git fetch https://github.com/googleforgames/agones.git pull/3439/head:pr_3439 && git checkout pr_3439
• helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.36.0-dev-e660011-amd64