Function run_join 

pub async fn run_join(
    link: Link,
    database: &Database,
    host: &dyn ClientHost,
    invitation: impl FnOnce() -> Result<Option<DeviceInvitation>>,
    replace: bool,
    progress: &(dyn Fn(Progress) + Sync),
) -> Result<(String, Outcome)>

Joins sync on a fresh database, or resumes the join it started, and returns the server. invitation is asked for only while enrollment is unfinished; None resumes the request this database already made. With replace, an invitation this join has not used becomes a new attempt from the same device keys; earlier attempts stay able to complete.