Explore deployment using shuttle

[joepio]

Shuttle is pretty cool. Compiles Rust apps to WASM, deploys it in one go. Supports actix, which is pretty cool, because WASM is single-threaded and actix is not.

However, we'll have to work around some things:

• No filesystem (used for storing attachments, database, search, config)

Shuttle has the "Shuttle persist" key value store. I don't think it supports range queries. Perhaps one day it will. Perhaps if it's also implemented by OpenDAL and we've implemented OpenDAL for everything, we could get most this in one go. #644

Only leaves search and config.