[RFC]: Metalog Distribution

### Description

This RFC proposes to add a [metalog](https://en.wikipedia.org/wiki/Metalog_distribution) distribution, based on the implementation provided by [rmetalog](https://github.com/isaacfab/rmetalog/). This implementation will include functions for:
- `quantile`
- `pdf`
- `cdf`
- `mean`

I've already started to make this contribution on my local machine.

### Related Issues

_No response_

### Questions

1. Metalog takes an array of coefficients as parameters. What is the standard way to pass arrays in stdlib? Would you be happy with just a JS array?
2. Metalog has two ways of construction, one is to provide coefficients, but it also really common to fit a distribution to samples via least squares regression. Where would the fitting functionality be provided in stdlib?
3. Would you accept a contribution of the metalog distribution?
4. Would you be ok if I created a draft PR so that you can see the changes that are being made to create a metalog distribution in stdlib? That way I can ask questions related to implementation there?

### Other

The implementation will be checked against the `rmetalog` package for accuracy.

### Checklist

- [X] I have read and understood the [Code of Conduct](https://github.com/stdlib-js/stdlib/blob/develop/CODE_OF_CONDUCT.md).
- [X] Searched for existing issues and pull requests.
- [X] The issue name begins with `RFC:`.

Start with this RFC and the rmetalog implementation it cites; resolve the coefficient-array and fitting API questions with maintainers before locating the distribution entry points. Done means an accepted Metalog distribution exposing quantile, pdf, cdf, and mean, with accuracy checked against rmetalog.

Do mô hình lập chỉ mục viết ra từ nội dung của issue.