Sticky routes documentation

[Kemi-Elizabeth]

Priority

1 - urgent - must be addressed immediately

Where should the changes be made?

Update https://docs.upsun.com/define-routes.html with sticky routes information.

What exactly should be updated?

https://docs.upsun.com/define-routes.html and https://fixed.docs.upsun.com/define-routes.html

Optional: Additional context

No response