Set cause on create index request in create from action (#124363)

In the create-index-from-source action, we should set the cause of the create index request so that it is clear in the logs. Without setting the cause on the request, the default value of api is used.

docs/changelog/124363.yaml

@@ -0,0 +1,5 @@
+pr: 124363
+summary: Set cause on create index request in create from action
+area: Data streams
+type: enhancement
+issues: []

x-pack/plugin/migrate/src/main/java/org/elasticsearch/xpack/migrate/action/CreateIndexFromSourceTransportAction.java

@@ -109,6 +109,7 @@ public class CreateIndexFromSourceTransportAction extends HandledTransportAction
         }
 
         var createIndexRequest = new CreateIndexRequest(request.destIndex()).settings(settings);
+        createIndexRequest.cause("create-index-from-source");
         if (mergeMappings.isEmpty() == false) {
             createIndexRequest.mapping(mergeMappings);
         }