dfr get-weekday for dataframe

Gets weekday from date.

Signature

> dfr get-weekday

Examples

Returns weekday from a date

> let dt = ('2020-08-04T16:39:18+00:00' | into datetime -z 'UTC');
    let df = ([$dt $dt] | dfr into-df);
    $df | dfr get-weekday
╭───┬───╮
│ # │ 0 │
├───┼───┤
│ 0 │ 2 │
│ 1 │ 2 │
╰───┴───╯