Reduce size of images in docs from 25MB to 13MB using pngquant
- Previous MR that used zopflipng https://gitlab.com/gitlab-org/gitlab-ce/merge_requests/4325
- Similar MR to another repo https://gitlab.com/gitlab-com/www-gitlab-com/merge_requests/3232
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data