Peer Reviews refresh pre Gartner approval

Commented out Gartner reviews in proofpoints.yml in advance of their review and approval of this content, using a future MR and its review app.

Prior to that

• checked links and removed expired Gartner and G2 reviews
• completed classification of reviews
• added data from Gartner ARO Peer Reviews for https://gitlab.com/gitlab-com/marketing/product-marketing/issues/948 at https://about.gitlab.com/handbook/marketing/product-marketing/peer-reviews/.