Support oft parent groups

app/Domains/Event/Actions/SignUp/SignUpCommand.php

@@ -61,6 +61,7 @@ class SignUpCommand {
                 'fee_type' => $this->request->feeType,
                 'sibling_reduction' => $this->request->siblingReduction,
                 'local_group' => $this->request->localGroup?->slug,
+                'parent_group_id' => $this->request->parentGroup?->id,
                 'birthday' => $this->request->birthday,
                 'address_1' => $this->request->address_1,
                 'address_2' => $this->request->address_2,