Security fix: Server-Side Request Forgery

[Ludy87]

Description

This PR enhances the isURLReachable method in the GeneralUtils class by:

1. Adding validation to restrict allowed protocols to http and https.
2. Introducing a helper method, isLocalAddress, to detect and exclude local addresses such as:
   • 127.0.0.1, localhost, and ::1 (loopback addresses)
   • Private IPv4 ranges (192.168.x.x, 10.x.x.x, 172.16.x.x - 172.31.x.x)
   • Link-local IPv6 addresses (fe80::/10).
3. Improving exception handling to return false for all invalid or unreachable URLs.

https://github.com/Stirling-Tools/Stirling-PDF/security/advisories/GHSA-4v4c-9hpr-93vx

Checklist

• I have read the Contribution Guidelines
• [] I have performed a self-review of my own code
• I have attached images of the change if it is UI based
• I have commented my code, particularly in hard-to-understand areas
• If my code has heavily changed functionality I have updated relevant docs on Stirling-PDFs doc repo
• My changes generate no new warnings
• I have read the section Add New Translation Tags (for new translation tags only)

[Ludy87]

@summerxxoo can you confirm that there are no other problems with SSRF?