Function fetch_sync_data 

async fn fetch_sync_data<'c>(
    transaction: &mut TransactedDb<'c>,
    session: &SessionInfo,
    initial: bool,
    sync_token: &mut SyncToken,
    filter_definition: Option<&FilterDefinition>,
) -> Result<Option<SyncData>, InternalServerError>

This function is a central point in which we query every possible data that needs synchronization.