Create test superuser when launching elasticsearch via 'run' task (#48072)

distribution/build.gradle

@@ -434,6 +434,7 @@ testClusters {
       setting 'xpack.sql.enabled', 'true'
       setting 'xpack.rollup.enabled', 'true'
       keystore 'bootstrap.password', 'password'
+      user username: 'elastic-admin', password: 'elastic-password', role: 'superuser'
     }
   }
 }