feat: add authz-adapter service and Envoy ext_authz integration

- Implemented authz-adapter deployment and service for Envoy gRPC authorization.
- Created PowerShell script to generate JWK for JWT authentication.
- Documented the integration of ext_authz with user-rpc.ValidateToken in ENVOY_EXT_AUTHZ_ADAPTER.md.
- Added comprehensive Envoy Gateway configuration guide with JWT authentication and access control in ENVOY_GATEWAY_GUIDE.md.

common/utils/responses.go

@@ -1,10 +1,20 @@
 package utils
 
+import "encoding/json"
+
 type ErrorResponse struct {
 	Code int    `json:"code"`
 	Msg  string `json:"msg"`
 }
 
+func (e *ErrorResponse) Error() string {
+	marshal, err := json.Marshal(e)
+	if err != nil {
+		return err.Error()
+	}
+	return string(marshal)
+}
+
 func NewErrorResp(code int, msg error) *ErrorResponse {
 	return &ErrorResponse{
 		Code: code,