Fix: Preserve on_connection_init.response policies when decoding WebBrokerApi xDS bindings

Summary

When decoding WebBrokerApi policies from xDS EventChannelResource in event-gateway/gateway-runtime/internal/xdsclient/handler.go, the current implementation treats on_connection_init only as a flat []interface{} and maps all policies into OnConnectionInit.Request. This means any xDS payload using the nested request/response form will silently drop response policies, which can never reach the runtime.

Fix Required

Update toWebBrokerApiBinding (and its per-channel equivalent) to accept both forms:

• If on_connection_init is a map[string]interface{} with request and/or response keys, decode each side separately into OnConnectionInit.Request and OnConnectionInit.Response.
• Otherwise, fall back to the existing flat-array behavior and populate Request for backward compatibility.

The same fix applies at both the API-level policies block and the per-channel policies block in toWebBrokerApiBinding.

References

• PR: https://github.com/wso2/api-platform/pull/1954
• Review comment: https://github.com/wso2/api-platform/pull/1954#discussion_r3239562654
• Related PR: https://github.com/wso2/api-platform/pull/1944

Requested by

@senthuran16