Fix broken links to docs
What does this MR do?
Fix most of broken links that appear on https://docs.gitlab.com according to https://gitlab.com/gitlab-com/gitlab-docs/builds/10032388
Do not update/delete: Banner broadcast message test data
Do not update/delete: Notification broadcast message test data
Fix most of broken links that appear on https://docs.gitlab.com according to https://gitlab.com/gitlab-com/gitlab-docs/builds/10032388