Function set_progress_comment 

pub fn set_progress_comment(
    conn: &Connection,
    provider: &str,
    entity: &str,
    local_id: i64,
    comment_id: Option<&str>,
) -> Result<()>

Record (or clear) the id of the living progress comment on a pairing.

Separate from upsert on purpose: the comment id has a different lifecycle from the sync bookkeeping — it is written when push creates or recreates the comment, and must survive every other sync untouched.