Add PostgreSQL dir with socket to Docker container as a volume

Also explicitly set path to pg_dump 9.6 to avoid using old 9.5 postgres
client.

Fixes: PROD-31827

Change-Id: I727073c1caec40f11b87afcd64e31cdc50185a83
diff --git a/backupninja/client/single.yml b/backupninja/client/single.yml
index 7bf8b7b..62279fe 100644
--- a/backupninja/client/single.yml
+++ b/backupninja/client/single.yml
@@ -3,6 +3,8 @@
 parameters:
   backupninja:
     client:
+      extra_params:
+        PGSQLDUMP: /usr/lib/postgresql/${_param:postgresql_major_version}/bin/pg_dump
       scheduling:
         when:
           - manual