Add httpx-secure to third party packages

[Zaczero]

Summary

Recently I worked on securing HTTPX against SSRF attacks (as none of the existing solutions worked for me) and decided to polish it up and publish it as a package for others to use.

Checklist

• I understand that this PR may be closed in case there was no previous discussion. (This doesn't apply to typos!)
• I've added a test for each change that was introduced, and I tried as much as possible to make a single atomic change.
• I've updated the documentation accordingly.

[lovelydinosaur]

Okay, thanks Kamil.

[Copilot]

Pull Request Overview

This PR adds documentation for a new third-party package called httpx-secure to the third party packages documentation. The package provides SSRF (Server-Side Request Forgery) protection functionality for HTTPX.

• Adds a new entry for httpx-secure package in the third party packages documentation

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