Document `errorCause` and `errorErrors`

**Feature to document**

Ref: https://github.com/webpack/webpack/pull/19453

**Author(s)**

Any

**Additional information**

`errorCause` outputs `cause` of any `Error` in stats
`errorErrors` outputs `errors` of `AggregateError` in stats

By default `true` for all

Possible values: `"auto"`/`true`/`false`

[ ] I am willing to work on this issue and submit a pull request.
