[RFC]: add `@stdlib/assert/is-palindrome`

### Description

This RFC proposes to add a new assert util to check if a string is palindrome or not.

### Related Issues

No.

### Questions

No.

### Other

Reference: [Palindrome | Wikipedia](https://en.wikipedia.org/wiki/Palindrome)

### 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:`.

The issue names no implementation file, test, or entry point. Start by locating existing @stdlib/assert utilities and their tests, then compare their conventions and confirm the palindrome behavior with maintainers before deciding what files define done.

Written by the indexing model from the issue text.