fix external snippet compatibility

Author: anandsyncs

docs/search/03-search-query-usage/code_snippets/03_0410_run_mongodb_tools_pod.sh

@@ -20,6 +20,7 @@ spec:
   - name: mongo-ca
     configMap:
       name: ${MDB_TLS_CA_CONFIGMAP}
+      optional: true
       items:
       - key: ca.crt
         path: ca.crt