Update GPT to follow new endpoint main target of 200ms

The MR changes GPT to use the new 200ms main target instead of the 500ms (gitlab-org/gitlab#330767 (closed)).

Additionally it adds the links to the new performance issues that were created for endpoints over 200ms.

• gitlab-org/gitlab#334434
• gitlab-org/gitlab#334435
• gitlab-org/gitlab#334437
• gitlab-org/gitlab#334438
• gitlab-org/gitlab#334439
• gitlab-org/gitlab#334443
• gitlab-org/gitlab#334444
• gitlab-org/gitlab#334445
• gitlab-org/gitlab#334446
• gitlab-org/gitlab#334447
• gitlab-org/gitlab#334448

Closes #455 (closed)