Rewrite the DSA-lobby backend in Rust

[Ma27]

To have a consistent code-base in the long run, it has been decided on our last sync a few weeks ago that the game-lobby API (currently written in C# and available in the old DiscoBot repo) should be ported to Rust as well.

With this change, we'll have even less components cluttered across several repos and can build (almost) the entire project in one run.

[TrueDoctor]

The API itself should be fairly trivial to implement. I suggest to use some framework like rocket for the api.
We have to build a new database structure as well to migrate away from firebase. I'd suggest to just use a postgres db.
On that note, should we provide a docker compose solution for easy deployment? (web api, database, rask-server)
And should we merge the web api and the game-server?

[TrueDoctor]

Should we provide a cli interface for the server?
this could be inspired by rask-server to save us some work
Alternatively, we could use a Rocket.toml as described here:
https://rocket.rs/v0.4/guide/configuration/