Added placeholder for lastName and role addition functionality

frontend/pshared/lib/data/dto/invitation/invitation.dart

@@ -9,11 +9,15 @@ part 'invitation.g.dart';
 class InvitationContentDTO {
   final String email;
   final String name;
+  @JsonKey(defaultValue: '')
+  //TODO remove when backend will accept lastName
+  final String lastName;
   final String comment;
 
   const InvitationContentDTO({
     required this.email,
     required this.name,
+    required this.lastName,
     required this.comment,
   });