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

Namespace: `@stdlib/stats/base/dists/gompertz`
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.

Reference implementations:

- [SciPy](https://docs.scipy.org/doc/scipy/reference/generated/scipy.stats.gompertz.html#scipy.stats.gompertz)

[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

Start by reviewing the existing packages under @stdlib/stats/base/dists and the proposed namespace @stdlib/stats/base/dists/gompertz, then compare the SciPy reference implementation. Done means adding the Gompertz distribution family with the PDF, CDF, quantile function, mean, median, and related evaluations described in the issue.

Written by the indexing model from the issue text.