Cast ID to string

[mzur]

There was the error Cannot assign string to property Biigle\Modules\MetadataCoco\Image::$id of type int here:

metadata-coco/src/Coco.php

Line 45 in 00e0e73

return Image::create($imageData);

Fix it with a cast and look for other places where the same error could occur.

[mzur]

Similar issue with the annotation ID here:

metadata-coco/src/Coco.php

Line 50 in 00e0e73

return Annotation::create($annotationData);