feat: Add onExportToBackend prop so host can handle it (#2612)

Co-authored-by: dwelle <luzar.david@gmail.com>

scripts/changelog-check.js

@@ -8,7 +8,7 @@ const changeLogCheck = () => {
         process.exit(1);
       }
 
-      if (!stdout || stdout.includes("packages/excalidraw/CHANGELOG.MD")) {
+      if (!stdout || stdout.includes("packages/excalidraw/CHANGELOG.md")) {
         process.exit(0);
       }