Instruct etcd to delete old revisions (patroni#3024)

Etcd keeps old revisions unless instructed to delete them. If we don't delete old revisions then etcd memory usage will keep growing forever due to keepalive updates. Since Patroni does not really need to roll back to older revisions we can safely delete them.

docker/entrypoint.sh

@@ -38,7 +38,7 @@ EOT
         exec dumb-init "$@"
         ;;
     etcd)
-        exec "$@" -advertise-client-urls "http://$DOCKER_IP:2379"
+        exec "$@" --auto-compaction-retention=1 -advertise-client-urls "http://$DOCKER_IP:2379"
         ;;
     zookeeper)
         exec /usr/share/zookeeper/bin/zkServer.sh start-foreground