Function register_worker 

pub async fn register_worker<E>(
    conn: &mut E,
    queue: &str,
    worker: &WorkerContext,
    last_seen: &Timestamp,
    backend_type: &str,
) -> Result<(), Error>
where
    for<'e> &'e mut E: Executor<'e, Database = Postgres>,

Register a worker in the database

Errors if worker already exists