[oba] use a database to store all orders

[josojo]

Initially, all orders will only be stored in memory. But in order to not lose all data after restarting and being able to store a lot of information, we should use a database:

probably, we should use the diesel library for it, just due to its popularity. But I am curious about your opinions.

diesel is not async, maybe we should switch to sqlx: We need to research a solution tbd