Save which user session created a compat session

This also exposes the user session in the GraphQL API, and allow
filtering on browser session ID on the app session list.

crates/data-model/src/compat/session.rs

@@ -80,6 +80,7 @@ pub struct CompatSession {
     pub state: CompatSessionState,
     pub user_id: Ulid,
     pub device: Device,
+    pub user_session_id: Option<Ulid>,
     pub created_at: DateTime<Utc>,
     pub is_synapse_admin: bool,
     pub last_active_at: Option<DateTime<Utc>>,