Enable prometheus pushgateway persistent storage

Change-Id: If539f26909bd56b168a806773bb9c6574c86bf40
Closes-bug: PROD-21073
diff --git a/metadata/service/pushgateway/container.yml b/metadata/service/pushgateway/container.yml
index 8d2e60e..0fff6f5 100644
--- a/metadata/service/pushgateway/container.yml
+++ b/metadata/service/pushgateway/container.yml
@@ -7,3 +7,5 @@
       bind:
         address: 0.0.0.0
         port: 9091
+      dir:
+        data: /srv/volumes/local/pushgateway