Adds helm schema validation test to the test suite

[igooch]

What type of PR is this?

/kind feature

What this PR does / Why we need it:

Final piece in the in-place upgrades moving to beta.

Adds a simple Helm schema validation test that runs as part of make test in CI / CD.

Note that this test only tests that the Helm values.yaml file passes the schema validation. It does not test if there have been changes to the Helm template that require changes to the validation schema.

Which issue(s) this PR fixes:

Closes #4093
Closes #3766

Special notes for your reviewer:

[agones-bot]

Build Failed 😭

Build Id: f8cf0c1a-e551-432f-8852-ae4a8ea6808b

Status: FAILURE

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[agones-bot]

Build Succeeded 🥳

Build Id: cc5060bc-7fca-45bc-ab4a-1a0b1ef3192a

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:1.47.0-dev-d9ef8ca
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.47.0-dev-d9ef8ca
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.47.0-dev-d9ef8ca-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.47.0-dev-d9ef8ca
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.47.0-dev-d9ef8ca
• Linux C++ SDK (build): agonessdk-1.47.0-dev-d9ef8ca-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.47.0-dev-d9ef8ca.zip

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

• https://d9ef8ca-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4101/head:pr_4101 && git checkout pr_4101
helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.47.0-dev-d9ef8ca

[lacroixthomas]

Can't approve, but LGTM, also tested locally