BE - Update createAiCatalogItemConsumer to add agents to group

When adding right now, we get this error:

Could not enable agent: GitLab Analytics Agent

Service account must be blank

This diff seems to fix the issue:

diff --git a/ee/app/services/ai/catalog/item_consumers/create_service.rb b/ee/app/services/ai/catalog/item_consumers/create_service.rb
index e0e24abd21eb..dcb684b7ba27 100644
--- a/ee/app/services/ai/catalog/item_consumers/create_service.rb
+++ b/ee/app/services/ai/catalog/item_consumers/create_service.rb
@@ -79,7 +79,7 @@ def create_item_consumer(service_account)
         def create_service_account
           # In case we don't need to create the service account (because this is not group level), we should return
           # no_op, and continue creating the item consumer.
-          return [:no_op, nil] if group.nil?
+          return [:no_op, nil] if group.nil? || item.agent?

           service_account_params = {
             namespace_id: group.id,