docs(assertion): add Supertest JavaScript assertion library

[ChyzhykTech]

Supertest is a popular HTTP assertion library for testing REST APIs, often used with other testing frameworks like Mocha or Jest

Checklist:

• I've read and understood Contributing Guidelines.
• I've added the new resource at the end of its section.
• This resource is out there for a while, and actively maintained.
• This resource is popular enough and has at least a few hundred stars on GitHub.

---

...

[gokaygurcan]

Thanks.