Remove use of alt-link and ensure homepage displays appropriate category links

From scaling agenda:

KENNY EricB Sid: Can we ensure that every shipped feature in the table on https://about.gitlab.com/ links to the docs? Usability testing linked to https://about.gitlab.com/direction/verify/usability_testing/ so please test others. EricB: I’ll take this one for the team and get a MR out today Here’s the MR: !35049 (merged) EricB: I’ve asked Todd B to merge as it changes our homepage Reverted in !36826 (merged) Kenny: We need to adjust the logic for how the link is selected on the homepage to select Product link first, then docs, then vision based on availability and remove the use of the alt-link. Also give error if it is no longer planned but there is no docs link. Kenny: Thumbs up, I’ll add the lint.

Tasks

• Banish Alt_Link - !36915 (merged)
• Add CI Check on categories.yml file - !37335 (merged)