Crash repl should remember session settings

[mfussenegger]

The REPL behavior of crash is now not intuitive because statements like SET search_path = .. seem to have no effect.

The reason for that is that crash uses crate-python. crate-python uses HTTP and CrateDB creates a new session per request. Because of that session settings are always discarded.

We could change this behavior on the server side for HTTP. But given that some clients use round-robin, starting to keep the session settings could result in confusing behavior as well. The session setting would be set on a single node, and a follow up request to another node wouldn't have it set.

We could migrate crash to use something like asyncpg to work around that.