Fix redirected links

Why is this change being made?

As external sites update their architecture, things get redirected, deleted, etc... and we want to make sure we don't have dead links in the docs. At the same time, redirected links aren't necessarily bad, but we want to make sure we aren't redirecting to a page that no longer lists the information, so it's good to update the redirected links as well.

This MR addresses certain links that return a permanent redirect.

Related gitlab-org/gitlab-docs#601 (closed)

Does this MR meet the acceptance criteria?

Assign to DRI

• Did you assign this change to the correct DRI of the page or information you are changing?

Conformity

• Added description to this MR explaining the reasons for the proposed change, per say-why-not-just-what