Function find_time_window_expr

async fn find_time_window_expr(
    plan: &LogicalPlan,
    catalog_man: CatalogManagerRef,
    query_ctx: QueryContextRef,
) -> Result<(String, Option<Expr>, TimeUnit, DFSchema), Error>

Return (the column name of time index column, the time window expr, the expected time unit of time index column, the expr’s schema for evaluating the time window)

The time window expr is expected to have one input column with Timestamp type, and also return Timestamp type, the time window expr is expected to be monotonic increasing and appears in the innermost GROUP BY clause

note this plan should only contain one TableScan