Allow caching to s3. #1

The two servers I'm planning on deploying the hosting service on are already part of my own s3 backbone. I'm thinking we could cache into the s3 to take advantage of redundancy and replication. The concern is that garage (my s3 solution) could be confused by say five hosting service instances trying to insert the same data at the same time. it should be fine though. Maybe i could have one firehose instance actually do the writing and keep this bucket be a way to bring a new instance up to speed. Right now the new instance is with an empty cache and has to wait for someone to request a site to download a copy. I was thinking of having it backfill from the DB but this is better and saves on DB calls