\XFI\Import\Impoter\vBulletin4::getAttachmentsGroupedByFile() is using hardcoded values

[Kirby]

Affected version

1.4.1

Method \XFI\Import\Impoter\vBulletin4::getAttachmentsGroupedByFile() is using hardcoded values for contentIdKey and contentType which does make it unusable for content types other than forum posts.
This seems inconsistent with other methods like \XFI\Import\Impoter\vBulletin4::getAttachmentsForFileDataIds() that can handle any content type.

It would be nice if this method could also support other content types.