Add throttle param to xtrabackup.client.single

Issue: PROD-22098
Change-Id: Ic024b37b92f363639e7fd25935f0edc28793bd75
diff --git a/xtrabackup/client/single.yml b/xtrabackup/client/single.yml
index cbe1123..25fa6d2 100644
--- a/xtrabackup/client/single.yml
+++ b/xtrabackup/client/single.yml
@@ -1,3 +1,9 @@
 classes:
 - service.xtrabackup.client.single
-- system.openssh.client.root
\ No newline at end of file
+- system.openssh.client.root
+parameters:
+  _param:
+    xtrabackup_client_throttle: 0 # disabled
+  xtrabackup:
+    client:
+      throttle: ${_param:xtrabackup_client_throttle}