Better styling for reference docs for JSON schema

[artberger]

The schema is a long JSON file that could be documented: https://github.com/agentgateway/agentgateway/blob/main/schema/local.json

Right now, it is in a table format: https://agentgateway.dev/docs/standalone/latest/reference/configuration/

But we would like a more interactive format for it. Inspiration: https://kubespec.dev/