Optimize the file storage structure of the knowledge base (#386)

packages/core/dataset/utils.ts

@@ -0,0 +1,8 @@
+import { datasetSpecialIds } from './constant';
+import { strIsLink } from '@fastgpt/common/tools/str';
+
+export function isSpecialFileId(id: string) {
+  if (datasetSpecialIds.includes(id)) return true;
+  if (strIsLink(id)) return true;
+  return false;
+}