Support domain-level redirects
### Summary GitLab Pages currently supports simple redirect rules. In https://gitlab.com/gitlab-org/gitlab-pages/-/merge_requests/458 we introduced support for splats and placeholders. We should look at supporting domain-level redirects. See https://docs.netlify.com/routing/redirects/redirect-options/#domain-level-redirects --- Proposal: - [x] Pages feature: https://gitlab.com/gitlab-org/gitlab-pages/-/merge_requests/936 - [x] Unit tests: https://gitlab.com/gitlab-org/gitlab-pages/-/merge_requests/936 - [x] Acceptance tests: https://gitlab.com/gitlab-org/gitlab-pages/-/merge_requests/936 - [x] Documentation: https://gitlab.com/gitlab-org/gitlab/-/merge_requests/138515 - [x] Feature Flag issue: https://gitlab.com/gitlab-org/gitlab-pages/-/issues/1087 Recording: ![Domain_Redirect](/uploads/78b93bc8f626c2c50d9226df2b28fe6a/Domain_Redirect.mov)
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