next.js

b1f45571 - Refactor GTM implementation to support google tag gateway (#81011)

Refactor GTM implementation to support google tag gateway (#81011) ### What? This PR refactors the Google Tag Manager implementation on `@next/third-parties`, it rewrites the implementation of the script url, params and types to allow `gtmId` to be optional when a script URL is provided. ### Why? Google released [Google Tag Gateway for Advertisers](https://developers.google.com/tag-platform/tag-manager/gateway/setup-guide?setup=manual) which allows first-party tracking on GTM. When running GTM using the current implementation, it doesn't work because the `?id=` is hardcoded into the implementation as it doesn't consider the possibility of tag gateway or any other setup where the ID is already part of the url. ### How? - Expanded the types - Refactored the initialisation of the script URL - Updated documentation relevant to GTM Closes #81009 Co-authored-by: JJ Kasper <jj@jjsweb.site>