feat: add session/prefix cache for doubao

relay/controller/text.go

@@ -31,6 +31,7 @@ func RelayTextHelper(c *gin.Context) *model.ErrorWithStatusCode {
 		return openai.ErrorWrapper(err, "invalid_text_request", http.StatusBadRequest)
 	}
 	meta.IsStream = textRequest.Stream
+	meta.Cache = len(textRequest.ContextId) > 0
 
 	// map model name
 	meta.OriginModelName = textRequest.Model