RFC: add the Tukey lambda distribution

## Checklist

> Please ensure the following tasks are completed before filing an issue.

- [x] Read and understood the [Code of Conduct][code-of-conduct].
- [x] Searched for existing issues and pull requests.
- [x] If this is a general question, searched the [FAQ][faq] for an existing answer.
- [x] If this is a feature request, the issue name begins with `RFC:`.

## Description

> Description of the issue (or feature request).

This RFC proposes adding the [Tukey lambda distribution](https://en.wikipedia.org/wiki/Tukey_lambda_distribution). Similar to other distribution namespaces, adding support for the Tukey lambda distribution would entail a family of packages for evaluating the PDF, CDF, quantile function, mean, median, etc.

Namespace: `@stdlib/stats/base/dists/tukey-lambda`
Reference: [`@stdlib/stats/base/dists/*`](https://github.com/stdlib-js/stdlib/tree/develop/lib/node_modules/%40stdlib/stats/base/dists)

## Related Issues

> Does this issue (or feature request) have any related issues?

No.

## Questions

> Any questions for reviewers?

No.

## Other

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

No.

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

[faq]: https://github.com/stdlib-js/stdlib/blob/develop/FAQ.md