Document what is needed to configure Project Browser to work in Production

Problem/Motivation

There is some specific configuration needed to make Project Browser work in a given environment (ex.g. Production). Namely, it needs:

• access to Composer
• access to a temporary area (should be fine)
• write access to the codebase itself (usually this is by the web user having write access to the entire codebase)

Proposed resolution

Write documentation for non-development (ex.g. not DDEV) setup, ex.g. for a new EC2 instance, which details all the steps necessary to make Project Browser work with the experimental UI.

NOTE: since much of this is actually related to what Package Manager does, these are also probably necessary for Automatic Updates to work, and such a page might already exist. So we can just link to that page for basic setup and then add Project-Browser-specific instructions on our own.

Also, this came out of the related issue 📌 [META] Test Project Browser on hosting providers Drupal people are using Active - which I realize will also help people know what hosts will allow Automatic Updates, for example. (So, is there also an issue for that over there? If not, they should glom on to our work here!)