[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:`.