Updated version mapping and post-release step

[kamaljeeti]

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: #4184

Closes #4184

Special notes for your reviewer:

[agones-bot]

Build Succeeded 🥳

Build Id: e8171218-5ecd-41a9-b158-362db7785509

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:1.50.0-dev-d1e84f6
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.50.0-dev-d1e84f6
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.50.0-dev-d1e84f6-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.50.0-dev-d1e84f6
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.50.0-dev-d1e84f6
• Linux C++ SDK (build): agonessdk-1.50.0-dev-d1e84f6-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.50.0-dev-d1e84f6.zip

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

• https://d1e84f6-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4191/head:pr_4191 && git checkout pr_4191
helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.50.0-dev-d1e84f6

[igooch]

LGTM