[FEATURE] Allow attachments in custom notifications via TypoScript

The existing possibility to add attachment to emails sent using the
extension has been extended, so attachments configured in TypoScript
now also can be applied to custom notifications. The configuration
options are the same as for emails sent by the registration process.

Example:

```
customNotifications {
    thanksForParticipation {
        title = Thank you message
        template = ThanksForParticipation.html
        subject = Thank you for participation in event "{event.title}"
        attachments {
          user {
            fromFiles {
              1 = fileadmin/test.pdf
            }
            fromEventProperty {
              1 = files
              2 = image
            }
            iCalFile = 1
          }
        }
    }
}
```

Classes/Service/Notification/AttachmentService.php

@@ -11,6 +11,7 @@
 
 namespace DERHANSEN\SfEventMgt\Service\Notification;
 
+use DERHANSEN\SfEventMgt\Domain\Model\Dto\CustomNotification;
 use DERHANSEN\SfEventMgt\Domain\Model\Registration;
 use DERHANSEN\SfEventMgt\Service\ICalendarService;
 use DERHANSEN\SfEventMgt\Utility\MessageType;
@@ -62,26 +63,31 @@ public function getAttachments(
         array $settings,
         Registration $registration,
         int $messageType,
-        string $messageRecipient
+        string $messageRecipient,
+        ?CustomNotification $customNotification = null
     ): array {
         $attachments = [];
         $settingPath = $this->getSettingsPath($messageType);
+        $attachmentSettings = $settings['notification'][$settingPath]['attachments'][$messageRecipient] ?? [];
 
-        if (isset($settings['notification'][$settingPath]['attachments'][$messageRecipient])) {
+        if ($customNotification) {
+            $attachmentSettings = $settings['notification']['customNotifications'][$customNotification->getTemplate()]['attachments'][$messageRecipient] ?? [];
+        }
+
+        if (!empty($attachmentSettings)) {
             // Attachments globally from TypoScript
-            $config = $settings['notification'][$settingPath]['attachments'][$messageRecipient];
-            $attachments = $this->getFileAttachments($config);
+            $attachments = $this->getFileAttachments($attachmentSettings);
 
             // Attachments from Event properties
             $eventAttachments = $this->getObjectAttachments(
-                $config['fromEventProperty'] ?? [],
+                $attachmentSettings['fromEventProperty'] ?? [],
                 $registration->getEvent()
             );
             $attachments = array_merge($attachments, $eventAttachments);
 
             // Attachments from Registration properties
             $registrationAttachments = $this->getObjectAttachments(
-                $config['fromRegistrationProperty'] ?? [],
+                $attachmentSettings['fromRegistrationProperty'] ?? [],
                 $registration
             );
             $attachments = array_merge($attachments, $registrationAttachments);
@@ -108,13 +114,19 @@ public function getICalAttachment(
         array $settings,
         Registration $registration,
         int $messageType,
-        string $messageRecipient
+        string $messageRecipient,
+        ?CustomNotification $customNotification = null
     ): string {
         $file = '';
         $settingPath = $this->getSettingsPath($messageType);
 
-        if (isset($settings['notification'][$settingPath]['attachments'][$messageRecipient]['iCalFile']) &&
-            (bool)$settings['notification'][$settingPath]['attachments'][$messageRecipient]['iCalFile']) {
+        $attachICalFile = (bool)($settings['notification'][$settingPath]['attachments'][$messageRecipient]['iCalFile'] ?? false);
+
+        if ($customNotification) {
+            $attachICalFile = (bool)($settings['notification']['customNotifications'][$customNotification->getTemplate()]['attachments'][$messageRecipient]['iCalFile'] ?? false);
+        }
+
+        if ($attachICalFile) {
             $file = GeneralUtility::tempnam(
                 'event-' . $registration->getEvent()->getUid() . '-',
                 '.ics'
@@ -188,6 +200,10 @@ protected function getObjectAttachments(array $propertyNames, AbstractEntity $ob
     protected function getAttachmentsFromProperty(AbstractEntity $object, string $propertyName): array
     {
         $attachments = [];
+        if ($propertyName === '') {
+            return $attachments;
+        }
+
         $property = $object->_getProperty($propertyName);
 
         if ($property instanceof ObjectStorage) {

Classes/Service/NotificationService.php

@@ -196,15 +196,17 @@ public function sendUserMessage(
                 $settings,
                 $registration,
                 $type,
-                MessageRecipient::USER
+                MessageRecipient::USER,
+                $customNotification
             );
 
             // Get iCal attachment if configured
             $iCalAttachment = $this->attachmentService->getICalAttachment(
                 $settings,
                 $registration,
                 $type,
-                MessageRecipient::USER
+                MessageRecipient::USER,
+                $customNotification
             );
 
             if ($iCalAttachment !== '') {