RFC: Add penguin dataset

## Checklist

> Please ensure the following tasks are completed before submitting a feature request.

- [x] Read and understood the [Code of Conduct][code-of-conduct].
- [x] Searched for existing issues and pull requests.
- [x] The issue name begins with `RFC:`.

## Description

> Description of the feature request.

This RFC proposes to add a penguin [dataset](https://github.com/allisonhorst/penguins) as an alternative to the iris dataset. This dataset could be added as `@stdlib/datasets/penguins`.

## Related Issues

> Does this feature request have any related issues?

None.

## Questions

> Any questions for reviewers?

No.

## Other

> Any other information relevant to this feature request? This may include screenshots, references, sample output, and/or implementation notes.

No.

[code-of-conduct]: https://github.com/stdlib-js/stdlib/blob/develop/CODE_OF_CONDUCT.md