Avoid N+1 query for channels with notes changes

Also, start work on new timing for recording observed notes edits.

Co-authored-by: Mikayla <mikayla@zed.dev>

crates/collab/src/db/tables/observed_buffer_edits.rs

@@ -9,6 +9,7 @@ pub struct Model {
     pub buffer_id: BufferId,
     pub epoch: i32,
     pub lamport_timestamp: i32,
+    pub replica_id: i32,
 }
 
 #[derive(Copy, Clone, Debug, EnumIter, DeriveRelation)]