Fix JSON Schema validation for ServiceAccount annotations

[0xaravindh]

What type of PR is this?

/kind bug

What this PR does / Why we need it:

• Updated serviceaccount.*.annotations schema to allow key-value string pairs.
• Changed additionalProperties from type: string to type: object.
• Resolves issue preventing Helm chart installation when annotations are provided.

Which issue(s) this PR fixes:

Closes #4119

Special notes for your reviewer:

[agones-bot]

Build Succeeded 🥳

Build Id: 24722a91-abd1-4d5c-8505-049d7bb8089f

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:1.48.0-dev-d43c88d
• image: us-docker.pkg.dev/agones-images/ci/agones-extensions:1.48.0-dev-d43c88d
• image: us-docker.pkg.dev/agones-images/ci/agones-sdk:1.48.0-dev-d43c88d-linux
• image: us-docker.pkg.dev/agones-images/ci/agones-ping:1.48.0-dev-d43c88d
• image: us-docker.pkg.dev/agones-images/ci/agones-allocator:1.48.0-dev-d43c88d
• Linux C++ SDK (build): agonessdk-1.48.0-dev-d43c88d-linux-arch_64.tar.gz
• SDK Server: agonessdk-server-1.48.0-dev-d43c88d.zip

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

• https://d43c88d-dot-preview-dot-agones-images.appspot.com/

To install this version:

git fetch https://github.com/googleforgames/agones.git pull/4122/head:pr_4122 && git checkout pr_4122
helm install agones ./install/helm/agones --namespace agones-system --set agones.image.registry=us-docker.pkg.dev/agones-images/ci --set agones.image.tag=1.48.0-dev-d43c88d