Developer experience: Make more use of SITE_URL and siteUrl env/config variables

[jackoconnordev]

Feature description

Make further use of the config.public.siteUrl across the website. In conjunction with setting SITE_URL environment variable this allows for developers to navigate around the website using the UI, without being forced to leave their local server.

This should just require string changes across each page's links.

Additional context

When running the website locally many navigation links take you away from your local server and bring you to the online version of the website.
The current workaround is to append the relative path to the page you want to localhost:3000 in the browser.
This is easy to forget and can lead to confusion as to whether the local or online version of the website is being viewed.

Examples

A link to providers page that does not keep user on localhost.

A link to providers page that keeps user on localhost.

Example of the proposed change

Needs clarification

Note: There are certain pages which do not exist on local host but are configured to use config.public.siteUrl.

Presumably they don't belong to this project so the resulting Error 404s are totally fine to see? The 404s can either be an indication for a developer that this page is not their concern, or else these urls can be changed to not use config.public.siteUrl and instead be hardcoded to point to the qiskit.org domain.