ai-proxy: support custom openai provider (#1176)

Co-authored-by: Kent Dong <ch3cho@qq.com>

plugins/wasm-go/extensions/ai-proxy/provider/request_helper.go

@@ -2,7 +2,6 @@ package provider
 
 import (
 	"encoding/json"
-	"errors"
 	"fmt"
 
 	"github.com/alibaba/higress/plugins/wasm-go/pkg/wrapper"
@@ -14,7 +13,7 @@ func decodeChatCompletionRequest(body []byte, request *chatCompletionRequest) er
 		return fmt.Errorf("unable to unmarshal request: %v", err)
 	}
 	if request.Messages == nil || len(request.Messages) == 0 {
-		return errors.New("no message found in the request body")
+		return fmt.Errorf("no message found in the request body: %s", body)
 	}
 	return nil
 }