Capture execution date time on dbt_results

[1yuv]

dbt_results is a helpful table to see the records of previous run, execution_time, and rows_affected. However, it doesn't have the date and time information of whe that run occured. This would help on estimating time and debugging any other issues.

Add a column execution_date on dbt_results table and capture either the start or end time. Better yet, it'd be good to have two columns with start_time and end_time.