Include rclone in jibri container

Hi there,

I would like to suggest including rclone in the jibri image.

It seems somewhat popular to patch the Dockerfile to include this change anyways. I was able to make a very simple finalize script with it for seafile.

A relatively small change with a lot of advantage considering it supports over 30 different backends.

#!/bin/sh
echo "Starting finalization"

rclone --config /config/rclone.conf \
	move /config/recordings/$(basename $1)/*.mp4 seafile:recordings

echo "Ending finalization"

Anyways, I was curious what others might think, before I submit something like a PR or raise an issue on Github.