Extracts EE-specific Merge Request feature specs to /ee

Docs: Add examples for linking to header IDs

Closes #57191

See merge request gitlab-org/gitlab-ce!26091

Docs: Fix anchors related to issues

See merge request gitlab-org/gitlab-ce!27165

Use US English for content

See merge request gitlab-org/gitlab-ce!27154

Fix code block not rendering

See merge request gitlab-org/gitlab-ce!27153

Use RECEIVE namespace rather than REQUEST

See merge request gitlab-org/gitlab-ce!27130

Fixed EE differences in noteable_note.vue

Closes gitlab-ee#9972

See merge request gitlab-org/gitlab-ce!27128

Fixed EE differences in noteable_note.vue

Closes #9972

See merge request gitlab-org/gitlab-ee!10646

Resolve "Extract EE specific files/lines for CI/CD spec/requests/api" CE

See merge request gitlab-org/gitlab-ce!27147

CE: Resolve "Extract EE specific files/lines for spec/features/boards"

See merge request gitlab-org/gitlab-ce!27110

Resolve "Extract EE specific files/lines for spec/features/boards"

Closes #6573

See merge request gitlab-org/gitlab-ee!10611

Add methods to check dead and retrying jobs

See merge request gitlab-org/gitlab-ce!27149

Reduce rspec retries

See merge request gitlab-org/gitlab-ce!26934

In both e2e QA tests and unit tests, reduce the number of retires
to 2 (i.e., 1 initial and one retry)

Use Rack::Utils.clean_path_info instead of copy-pasted version.

See merge request gitlab-org/gitlab-ce!27001

Resolve Environments#additional_metrics TypeError, ensure unix format

Closes #60162

See merge request gitlab-org/gitlab-ce!27118

Fix the bug that the project statistics is not updated

See merge request gitlab-org/gitlab-ce!26854

EE port of fixing the bug that the project statistics is not updated

See merge request gitlab-org/gitlab-ee!10626

Merge branch '10918-follow-up-from-docs-improve-to-include-using-sidekiq-cluster-via-gitlab-rb' into 'master'

Resolve "Follow-up from "Docs: Improve to include using sidekiq-cluster via gitlab.rb""

Closes #10918

See merge request gitlab-org/gitlab-ee!10645

Fix page specific JavaScript link in documentation

See merge request gitlab-org/gitlab-ce!27162

Update auth with registry docs

See merge request gitlab-org/gitlab-ce!27148

Add environment url validation

Closes #46326

See merge request gitlab-org/gitlab-ce!26805

Create pipelines for merge requests **only** when source branch is updated

See merge request gitlab-org/gitlab-ce!26921

Prevent merge if the merge request pipeline is stale

Closes #7380

See merge request gitlab-org/gitlab-ee!9643

Add endpoint for Jira to request user information

Closes #10752

See merge request gitlab-org/gitlab-ee!10482

Also reduced a bit of duplication and
created a user.json schema file which
is referenced by pull_request.json and
pull_requests.json references
pull_request.json now.
Moved content of "url" field to "html_url"

According to https://developer.github.com/v3/users the "url" field
should contain an api url - not the html url.

Additionally Jira Pull Requests are now showing an avatar of the PR
author.

Add changelog entry

Add missing mr number

Add specs

Expose url of user in url and html_url

I decided against returning an empty string for url (which is,
according to api documentation, supposed to return an api endpoint
instead of a user profile page) but make it return the profile page
as before so the changes won't break any existing code.

Remove extra blank line