Fix live assistance redirect and wording

Why is this change being made?

The name and path were changed in gitlab-com/marketing/digital-experience/buyer-experience!381 (merged)

This change is to resolve the 404 error when visiting the old URLs. In addition, it updates the files containing live-upgrade-assistance to be upgrade-assistance.

Note: I am unsure about the index.html at the end for the redirect file, I wasn't able to test this locally due to m1 not being able to install the SSL gem.

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