Adjust converting guide to add section about moving domains

[Kemi-Elizabeth]

Priority

2 - Important - inaccurate info needs to be corrected to prevent customer issues

Where should the changes be made?

https://docs.upsun.com/learn/tutorials/migrating/from-fixed.html

What exactly should be updated?

Aadd a section about moving the domain name from PSH to Upsun in the page.

Optional: Additional context

No response