Add audit plugin: my_xss_test example for reflected XSS

[PoornimaBaste]

Summary

This PR adds a new audit plugin my_xss_test that detects reflected XSS
vulnerabilities using a simple payload.

How to test

1. Start a target website (DVWA, Mutillidae, or any HTTP server).
2. Enable plugin in w3af console:
   plugins audit my_xss_test
   plugins discovery web_spider
   target set target http://localhost:8000
   start

Notes

• This is an example plugin to demonstrate how to write an audit plugin.
• Only one payload is tested for reflection.

Author

<Poornima / https://github.com/PoornimaBaste>