Deliver videos through CDN

[rmil]

Currently we are still relying on nginx to deliver our videos, so ideally we want to swap it over to our "cdn" which will hopefully make our video pipeline a little bit more flexible.
We'll need to configure the buckets so it would be read-only for unauthorised users (unless we gave everyone signed urls but that is effort). An example of what a working download url would look like: https://cdn.ystv.co.uk/minio/download/live/clip.mkv?token=

With regards to migrating the video library, I'm probably going to hold off for now but just essentially trick Minio through mouting and symbolic links that it's in it's library but it's still on web until we've migrated over.