Dedupe nextjs adapter

[YazeedLoonat]

What is this feature or what feature is this part of?
This is a spin off of: #3357

currently we have duplicated code the [...backendUrl.ts] files on the partner and public site. This is a ticketo to dedupe this and move the code into the shared-helpers folder.

Cannot find module 'node:url' from 'node_modules/http-cookie-agent/dist/http/create_cookie_agent.js' is the error we were running into when first attempting it. Which from reading https://stackoverflow.com/questions/73303447/cannot-find-module-nodeurl-when-executing-typescript-from-webstorm seems to be a problem between jest and node's url module.
https://stackoverflow.com/questions/75508376/jest-does-not-recognize-typeerror-thrown-by-url-constructor has a few examples of this not working as well as jestjs/jest#2549 (comment) which has a possible solution which didn't work when attempted.