Try to switch to from actix to tokio runtime

[khorolets]

At the moment we mix actix and tokio runtimes.

Historically diesel works synchronously while we need it asynchronous. We use actix-diesel library because the alternative tokio-diesel just didn't work. That's the reason we wrap our main with [actix::main], but everywhere else we explicitly use tokio.

It would be nice to try to switch to tokio completely to avoid mixing things up and make our codebase and dependencies a bit clearer.

It might not work and we could live with that, so this issue is "like-to-have" more that "must-have"