Updates for SLL7 LTSS

[tahliar]

PR creator: Description

The SLL7 guides needed some updates for LTSS.

• I've reduced the SMT guide down to a stub stating it is not supported, and linking to a procedure to migrate to RMT.
• I've updated the Lite guide with the new repos, but I haven't added all the Important boxes as it was already an LTSS product.
• The new RMT script isn't available yet, so I've added it directly to the guide. It's quite long this time so I added it to an appendix that we can reuse whenever this is needed.
• Re-registration might not be working as expected so I've temporarily commented out those parts of the warnings. But they are there in the diff, and will be quick to add when it's ready.

PDFs:

Main RMT guide:
art-quickstart_en.pdf

Lite guide:
art-lite-quickstart_en.pdf

SMT guide:
art-quickstart-smt_en.pdf

PR creator: Are there any relevant issues/feature requests?

• Jira Issue #SLL-363

PR creator: Which product versions do the changes apply to?

When opening a PR, check all versions of the documentation that your PR applies to.

• SLL 9 (current main, no backport necessary)
• SLL 8
• SLL 7

PR reviewer only: Have all backports been applied?

The doc team member merging your PR will take care of backporting to older documents.
When opening a PR, do not set the following check box.

• all necessary backports are done

[tahliar]

After discussion, this is ready to go. Remaining TODOs are for tomorrow.