dfr get-year for dataframe

Gets year from date.

Signature

> dfr get-year

Examples

Returns year 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-year
╭───┬──────╮
│ # │  0   │
├───┼──────┤
│ 0 │ 2020 │
│ 1 │ 2020 │
╰───┴──────╯