Fix 500 error while navigating to the `pages_domains` 'show' page.

Closes #1447 and #1448

See merge request !993

==================
= Implementation =
==================

1. The path of the page is of the form 'group/project/pages/domains/<domain_name>'
2. Rails looks at `params[:id]` (which should be the domain name), and finds the
   relevant model record.
3. Given a domain like `foo.bar`, Rails sets `params[:id]` to `foo` (should be
   `foo.bar`), and sets `params[:format]` to `bar`
4. This commit fixes the issue by adding a route constraint, so that
   `params[:id]` is set to the entire `foo.bar` domain name.

=========
= Tests =
=========

1. Add controller specs for the `PagesDomainController`. These are
   slightly orthogonal to this bug fix (they don't fail when this bug is
   present), but should be present nonetheless.
2. Add routing specs that catch this bug (by asserting that the `id`
   param is passed as expected when it contains a domain name).
3. Modify the 'RESTful project resources' routing spec shared example to
   accomodate controllers where the controller path (such as
   `pages/domains`) is different from the controller name (such as
   `pages_domains`).

[ci skip]

[ci skip]

CE upstream

See merge request !991

CE upstream

Closes gitlab-ce#25843, gitlab-ce#25832, and gitlab-ce#25257

See merge request !986

Fix lookup of project by unknown ref when caching is enabled

Closes #24224

See merge request !7988

Whitelist next project names: notes, services

See merge request !8239

Exclude non existent repository storages.

See merge request !8244

fixed minor animation glitch in mini pipeline graph animation

See merge request !8243

Resolve "KaTeX fonts 404 on gitlab.com"

Closes #25896

See merge request !8228

Update Bitbucket callback URL documentation

Closes #25950

See merge request !8241

Resolve "Remove Builds tab from Merge Requests and Commits"

Closes #23638

See merge request !7763

Closes #25950

[ci skip]

Auto deploy

Closes #23580

See merge request !8135

Put back progress bar CSS

Closes #25938

See merge request !8237

Resolve "Titles are bigger than usual"

Closes #25906

See merge request !8235

Change code font size to 12px

See merge request !8157

Backport moving MR widget CI JS out of script tag

See merge request !8200

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Filter protocol-relative URLs in ExternalLinkFilter. Fixes issue #22742.

Closes #22742

See merge request !6635

[EE] Allow unauthenticated access to Repositories & Repository Files API GET endpoints

See merge request !985

Add changelog entry