Avoid exceeding Kubernetes object size limits for Authorization config storage

[zhaohuabing]

Not for this PR, but for the future:
This config is stored on a k8s secret, and in scenarios where there are many MCPRoutes and many Authorization rules, the contents may exceed the max sicze of a k8s object.
We may need to come up with a different way to store this to avoid reaching these limits. We'll create a follow-up issue to track this.

Originally posted by @nacx in #1482 (comment)

[mathetake]

I think this is not a priority at this point. Once we migrate to the core MCP API, the configuration will be distributed as a pure envoy filter config via extension server, hence no secret as a middle man vs now.