Investigate database backups

[Mirko-von-Leipzig]

We need some way of creating backups of the current state of the store.

I'm aware of https://litestream.io/ which stream sqlite using its WAL file. From what I recall it requires careful tweaking of WAL settings but maybe that's improved by now. I also recall the guarantees not being 100% i.e. it could miss things if the WAL updates too fast.

We should also investigate alternatives..

• do it via gRPC proxy code i.e. duplicate the store write messages