[BUG] Reading of collections from database doesn't work

[beatrycze-volk]

Description

Reading of collections from database doesn't work in MetadataController.

Expected Behavior

The collections should be read correctly from database and displayed to the frontend.

Screenshots and Examples

Argument $value is a string not and array.

    private function parseCollections(int $i, $value, array &$metadata) : void
    {
        $j = 0;
        foreach ($value as $entry) {
            $collection = $this->collectionRepository->findOneByIndexName($entry);
            if ($collection) {
                $metadata[$i]['collection'][$j] = $collection->getLabel() ? : '';
                $j++;
            }
        }
    }

Additional Context

Related to #1314 and #1308