Add reference to PHP client on Bulk API page (#78558) (#78651)

Co-authored-by: James Rodewig <40268737+jrodewig@users.noreply.github.com>

Co-authored-by: Christian Fratta <christian.fratta@gmail.com>

docs/reference/docs/bulk.asciidoc

@@ -142,6 +142,9 @@ JavaScript::
 .NET::
     See https://www.elastic.co/guide/en/elasticsearch/client/net-api/current/indexing-documents.html#bulkall-observable[`BulkAllObservable`]
 
+PHP::
+    See https://www.elastic.co/guide/en/elasticsearch/client/php-api/current/indexing_documents.html#_bulk_indexing[Bulk indexing]
+
 [discrete]
 [[bulk-curl]]
 ===== Submitting bulk requests with cURL