fix: define primary key when adding documents

If we do not define the primary key when adding documents, MeiliSearch does not know which should be the primary key

Find more information here:
https://www.meilisearch.com/docs/learn/core_concepts/primary_key#meilisearch-guesses-your-primary-key

Classes/Service/IndexService.php

@@ -46,7 +46,7 @@ public function add(Document $document)
         try {
             if ($this->client->isHealthy()) {
                 $index = $this->client->index($this->index);
-                $index->addDocuments($document->toArray());
+                $index->addDocuments($document->toArray(), 'id');
             } else {
                 $this->logger->warning('MeiliSearch is not healthy.');
             }