Continuously backup the database instead of batch backups

[CamDavidsonPilon]

Consider something like litestream

Pros:

• no need for heavy backup jobs (#81)
• always up to date data replicas, instead of every N days
• delete our own internal backup code

Cons:

• how does litestream deal with a replica being unavailable?
• more cpu work upfront during an experiment
• more overhead during an experiment

[CamDavidsonPilon]

One problem is that I don't know the hostname of a worker in the cluster apriori to setting up litestream. Also I can't gauruntee it's always available and online.

This could be solved by specifying it in the config.ini - maybe this is a plugin and not a builtin feature.

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Alternatively, litestream could backup cont. locally to ~/.pioreactor/storage, and every N days, bulk back up to other machines.