Added Muti Site URL Handling under Common Pitfalls section

[NikithaBasavanna]

📋 Description

Added a new section documenting Muti Site URL Handling under Common Pitfalls section

📎 Related Issues (if applicable)

✅ Contributor Checklist

I've followed the Umbraco Documentation Style Guide and can confirm that:

• [*] Code blocks are correctly formatted.
• [*] Sentences are short and clear (preferably under 25 words).
• [*] Passive voice and first-person language (“we”, “I”) are avoided.
• [*] Relevant pages are linked.
• [*] All links work and point to the correct resources.
• [*] Screenshots or diagrams are included if useful.
• [*] Any code examples or instructions have been tested.
• [*] Typos, broken links, and broken images are fixed.

Product & Version (if relevant)

CMS 13-17

Deadline (if relevant)

📚 Helpful Resources

• 🧾 Umbraco Contribution Guidelines
• ✍️ Umbraco Documentation Style Guide

[sofietoft]

Thanks for the PR @NikithaBasavanna !

Does this need an internal technical review from our developers?
If so, could you please share it in the umbraco-cms channel on our internal Slack?

Also, I noticed quite a few code elements and snippets without code formatting.
Could you please go through it and ensure that all code bits and pieces are correctly formatted?

I'll give it a full review after the technical review (if that's needed).