supported attachment upload

app/lib/db-types.ts

@@ -1,5 +1,13 @@
 import { ObjectId } from "mongodb";
 
+export interface BillAttachment {
+    fileName: string;
+    fileSize: number;
+    fileType: string;
+    fileLastModified: number;
+    fileContentsBase64: string;
+};
+
 /** Bill basic data */
 export interface LocationBase {
     name: string;
@@ -25,7 +33,8 @@ export interface PlainLocation {
 export interface BillBase {
     name: string;
     paid: boolean;
-    document?: string|null;
+    attachment?: BillAttachment|null;
+    notes?: string|null;
 };
 
 /** bill object in the form returned by MongoDB */