Function build_pk_from_aggr 

fn build_pk_from_aggr(plan: &LogicalPlan) -> Result<Option<TableDef>, Error>

Return first timestamp column which is in group by clause and other columns which are also in group by clause

Returns

• Option<String> - first timestamp column which is in group by clause
• Vec<String> - other columns which are also in group by clause

if no aggregation found, return None