Stub Rails.application.env_config to prevent spec failures

Closes gitlab-ee#8488

See merge request gitlab-org/gitlab-ce!23222

Change link to help broken link checker

See merge request gitlab-org/gitlab-ce!23220

When we modify env_config, that is on the global Rails.application, and
we need to stub it and allow it to be modified in-place, without
polluting later tests.

When we modify env, then the context is a request, or something else
that only lives for a single spec.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/8488

Refine cursor positioning in Markdown Editor for wrap tags.

Closes #54015

See merge request gitlab-org/gitlab-ce!23085

Remove unused partial

See merge request gitlab-org/gitlab-ce!23180

Show what RPC is called in the performance bar

See merge request gitlab-org/gitlab-ce!23140

Update docs for include to mention 'allow requests to local network' requirement

Closes #53595

See merge request gitlab-org/gitlab-ce!23055

Enable even more frozen string for lib/gitlab

See merge request gitlab-org/gitlab-ce!23161

Bump nokogiri, loofah, and rack gems for security updates

See merge request gitlab-org/gitlab-ce!23204

Bump ruby_parser to 3.11.0 for Ruby 2.5 compatibility

See merge request gitlab-org/gitlab-ce!23209

Rails5 deprecation: Passing a class as a value in an Active Record query is deprecated

See merge request gitlab-org/gitlab-ce!23164

loofah: CVE-2018-16468:
https://github.com/flavorjones/loofah/issues/154

nokogiri: CVE-2018-14404 and CVE-2018-14567
https://github.com/sparklemotion/nokogiri/blob/master/CHANGELOG.md

rack: CVE-2018-16471
https://github.com/rack/rack/commit/e5d58031b766e49687157b45edab1b8457d972bd

i18n: https://github.com/svenfuchs/i18n/releases

concurrent-ruby: https://github.com/ruby-concurrency/concurrent-ruby/blob/master/CHANGELOG.md

CE port of "qa-staging-15-use-existing-users-ee"

See merge request gitlab-org/gitlab-ce!22864

add guide for creating runbook

See merge request gitlab-org/gitlab-ce!22885

See https://github.com/seattlerb/ruby_parser/blob/master/History.rdoc

Fix typo in js (props, specs)

See merge request gitlab-org/gitlab-ce!23103

Increase rspec parallelization to 50

See merge request gitlab-org/gitlab-ce!23149

Update merge request file tree docs

See merge request gitlab-org/gitlab-ce!23187

Match users better by their private commit email

Closes #54046

See merge request gitlab-org/gitlab-ce!23080

Backport of ee/8120: Smartcard authentication

See merge request gitlab-org/gitlab-ce!23012

Upgrade @gitlab/svg to 1.38.0

See merge request gitlab-org/gitlab-ce!23177

Improve variables support

See merge request gitlab-org/gitlab-ce!23077

Add support for surfacing a link to the branch or tag name in push message…

Closes #51959

See merge request gitlab-org/gitlab-ce!22651

The disabling of Gitaly was basically stubbing `Feature.enabled?` call,
which was never triggered.

This ensures that variables accept only string,
alongside also improves kubernetes_namespace,
improving validation and default value being set.

Private commit emails were introduced in !22560, but some parts of
GitLab were not updated to take account of them. This commit adds
support in places that were missed.

Refactor Member#add_user for GitLab EE

See merge request gitlab-org/gitlab-ce!23119

Fix some "Introduced in" inconsistencies

See merge request gitlab-org/gitlab-ce!23154

Documentation: update Libre -> Core

See merge request gitlab-org/gitlab-ce!22533

Update the cluster docs for Knative

See merge request gitlab-org/gitlab-ce!23113