RFC: add deep-pick

## 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 proposal recommends adding the utility `@stdlib/utils/deep-pick`. The utility would extend the behavior of `@stdlib/utils/pick` to deeply nested object properties, as well as provide support for deep copying. The current `@stdlib/utils/pick` only supports shallow copy of first-level properties.

## 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/master/CODE_OF_CONDUCT.md
[faq]: https://github.com/stdlib-js/stdlib/blob/master/FAQ.md