move preservePath property to root options (#38486)

types/multer/index.d.ts

@@ -43,9 +43,9 @@ declare namespace multer {
             parts?: number;
             /** For multipart forms, the max number of header key=> value pairs to parse Default: 2000(same as node's http). */
             headerPairs?: number;
-            /** Keep the full path of files instead of just the base name (Default: false) */
-            preservePath?: boolean;
         };
+        /** Keep the full path of files instead of just the base name (Default: false) */
+        preservePath?: boolean;
         /** A function to control which files to upload and which to skip. */
         fileFilter?(req: Express.Request, file: Express.Multer.File, callback: (error: Error | null, acceptFile: boolean) => void): void;
     }