feat(server): return asset checksum (#2582)

* feat: return asset checksum

* chore: generate open api

* chore: coverage

* feat(server): support base64 hashes in bulk upload check:

* chore: generate open api

mobile/openapi/test/asset_bulk_upload_check_item_test.dart

@@ -21,6 +21,7 @@ void main() {
       // TODO
     });
 
+    // base64 or hex encoded sha1 hash
     // String checksum
     test('to test the property `checksum`', () async {
       // TODO