docs: fix serveless example (#373)

Author: paulohtb6

modules/manage/partials/controlplane-api.adoc

@@ -295,9 +295,11 @@ Create a Serverless cluster by making a request to xref:api:ROOT:cloud-controlpl
 curl -H 'Content-Type: application/json' \
 -H "Authorization: Bearer <token>" \
 -d '{
-  "name": <serverless-cluster-name>,
-  "resource_group_id": <resource-group-id>,
-  "serverless_region": "us-east-1"
+  "serverless_cluster": {
+    "name": "<serverless-cluster-name>",
+    "resource_group_id": "<resource-group-id>",
+    "serverless_region": "us-east-1"
+  }
 }' -X POST https://api.redpanda.com/v1/serverless/clusters
 ----