Add schema validation support for WebBrokerApi in DeployAPIConfiguration

[coderabbitai]

Summary

The WebBrokerApi branch in DeployAPIConfiguration (gateway/gateway-controller/pkg/utils/api_deployment.go) currently bypasses schema validation. Malformed configs (e.g., invalid policy version patterns) can be persisted and only fail later during snapshot or runtime translation.

Required work

• Extend the config.Validator to support api.WebBrokerApi.
• Uncomment and enable the s.validator.Validate(&c) call in the api.WebBrokerApi case of the post-render validation switch.
• Ensure invalid payloads are rejected at the REST API layer with a structured ValidationErrorListError response.

Context

• Raised in PR Add implementation for WebBrokerAPIs #1954 (comment: Add implementation for WebBrokerAPIs #1954 (comment)) by @coderabbitai.
• Related discussion also tracked in PR [DO NOT MERGE] Add Implementation for Exposing Brokers as Subscribable APIs over Web-friendly Protocols #1944.
• Requested by: @senthuran16