Update template files from latest zalando image

auth_file.txt.tmpl

@@ -1,2 +1 @@
 "$PGUSER" "$PGPASSWORD"
-"$STATS_USER" "$STATS_PASSWORD"

pgbouncer.ini.tmpl

@@ -7,10 +7,10 @@
 pool_mode = $CONNECTION_POOLER_MODE
 listen_port = $CONNECTION_POOLER_PORT
 listen_addr = *
-auth_type = plain
+auth_type = md5
 auth_file = /etc/pgbouncer/auth_file.txt
 admin_users = $PGUSER
-stats_users = $STATS_USER
+stats_users_prefix = robot_
 auth_query = SELECT * FROM $PGSCHEMA.user_lookup($1)
 logfile = /var/log/pgbouncer/pgbouncer.log
 pidfile = /var/run/pgbouncer/pgbouncer.pid
@@ -30,7 +30,14 @@ default_pool_size = $CONNECTION_POOLER_DEFAULT_SIZE
 
 # Add more server connections to pool if below this number. Improves behavior
 # when usual load comes suddenly back after period of total inactivity.
-min_pool_size = $CONNECTION_POOLER_MIN_SIZE
+#
+# NOTE: This value is per pool, i.e. a pair of (db, user), not a global one.
+# Which means on the higher level it has to be calculated from the max allowed
+# database connections and number of databases and users. If not taken into
+# account, then for too many users or databases PgBouncer will go crazy
+# opening/evicting connections. For now disable it.
+#
+# min_pool_size = $CONNECTION_POOLER_MIN_SIZE
 
 # How many additional connections to allow to a pool
 reserve_pool_size = $CONNECTION_POOLER_RESERVE_SIZE