docs: single page for _In a restricted environment_

[themr0c]

What does this PR do?

docs: single page for Installing and setting up in a restricted environment

• One single page.
• Simplified outline around the expected most common story.
• Presented variations to minimize distractions:
  • OS variations in tabs. The user sees only steps for the OS they are using.
  • Optional steps in foldable details. By default, the user does not see the least common steps.

Screenshot / video of UI

What issues does this PR fix or reference?

fixes #4269

How to test this PR?

[themr0c]

This pull request has received enough comments and is ready to merge. Can you merge it, please?

[themr0c]

The Argos test requires a file that does not exist. I believe the Argos test itself is broken, not this pull request.

[themr0c]

I will continue rebasing and fixing the increasing number of conflicts and errors once I receive an agreement on the content. It makes no sense investing time in this activity if the team has no plan to accept the pull request.

[benoitf]

the website is not building with that change

[themr0c]

Okay, I understand that with the latest changes in tooling, the presence of links to redirected pages, which was fine before, is causing build errors. I will update the PR with fixes on the redirects to pass the build.

[themr0c]

The last commit should fix the broken links.