CustomInputModifier: delay obtaining id until form attachment

`Container::addDynamic` from `Kdyby/Replicator` would only run the closure passed to it after the form is attached.
This is not the case with `contributte/forms-multiplier`, which runs it during creation, which would result in throwing the following `InvalidStateException`:

    Component 'registry_address' is not attached to 'Nette\Forms\Form'.

Let’s wait until the form is attached before trying to obtain the input’s id.

app/Config/CustomInputModifier.php

@@ -14,14 +14,18 @@ final class CustomInputModifier implements InputModifier {
 	public static function modify(Control $input, IContainer $container): void {
 		// we also have some inputs that are based on Nextras\FormComponents\Fragments\UIComponent\BaseControl
 		if ($input instanceof BaseControl && $input->getName() === 'registry_address') {
-			$pairId = 'pair-' . $input->htmlId;
-			$input->setOption('id', $pairId);
+			$input->monitor(Form::class, function(Form $form) use ($input, $container): void {
+				// ID is not available until the Form is attached.
+				// Note: This will not handle re-attaching the form under different name but entries do not do that.
+				$pairId = 'pair-' . $input->htmlId;
+				$input->setOption('id', $pairId);
 
-			/** @var BaseControl */
-			$country = $container->getComponent('country');
-			$country->addCondition(Form::NOT_EQUAL, 46)->toggle($pairId, false);
-			$input->setRequired(false);
-			$input->addConditionOn($country, Form::EQUAL, 46)->setRequired();
+				/** @var BaseControl */
+				$country = $container->getComponent('country');
+				$country->addCondition(Form::NOT_EQUAL, 46)->toggle($pairId, false);
+				$input->setRequired(false);
+				$input->addConditionOn($country, Form::EQUAL, 46)->setRequired();
+			});
 		}
 	}
 }