feat: add useRequestHeaders hook

[DustinJSilk]

What is it?

• Feature / enhancement
• Bug
• Docs / tests

Description

I've added a new hook to Qwik City to expose request headers during SSR - useRequestHeaders

This hook can be used by applications that rely on external APIs that require authentication tokens. Tokens can be stored as a cookie and then retrieved during SSR in a useResource$ hook and passed on to the API.

Currently, the only way to access headers is in the onGet methods.

Use cases and why

• 1. SPAs that use a GraphQL API that want to make use of SSR without adding onGet(/etc) methods will use the useResource$ hook to run queries from both environments but need to forward the access tokens onto the API.

Checklist:

• My code follows the developer guidelines of this project
• I have performed a self-review of my own code
• I have made corresponding changes to the documentation
• Added new tests to cover the fix / functionality