Prevent concurrent execution of PipelineScheduleWorker

Closes gitlab-com/gl-infra/production#805

See merge request gitlab-org/gitlab-ce!27781

Change comments to point to the new path of sidekiq-cluster

See merge request gitlab-org/gitlab-ce!27707

Upgrade letter_opener_web to support Rails 5.1

See merge request gitlab-org/gitlab-ce!27829

Before this commit using `/rails/letter_opener` in `development`
environment failed with:

    undefined method `before_filter'

See https://github.com/fgrehm/letter_opener_web/issues/68

This commit upgrades `letter_opener_web` to 1.3.4 so Rails 5.1 is
supported.

Add full backtrace for RSpec output

See merge request gitlab-org/gitlab-ce!27686

Upgrade Gitaly to v1.36.0

See merge request gitlab-org/gitlab-ce!27831

Make `CI_COMMIT_REF_NAME` and `SLUG` variable idempotent

Closes #60822

See merge request gitlab-org/gitlab-ce!27663

Move test method to the bottom

See merge request gitlab-org/gitlab-ce!27816

Internationalisation of cycle_analytics directory

See merge request gitlab-org/gitlab-ce!27674

This is one of many MRs opened in order to improve the overall
internationalisation of the GitLab codebase.

i18n documentation
https://docs.gitlab.com/ee/development/i18n/externalization.html

Format extra help page text like wiki

Closes #55948

See merge request gitlab-org/gitlab-ce!26782

CE Backport: Prefer usage of helper `expanded_by_default?`

See merge request gitlab-org/gitlab-ce!27729

Stop using `Rails.env.test?` in views.

CE: Fixes EE differences for app/views/projects/new.html.haml

See merge request gitlab-org/gitlab-ce!27617

Use keyword args for databuilder push

See merge request gitlab-org/gitlab-ce!24088

Internationalisation of groups directory

See merge request gitlab-org/gitlab-ce!27679

This is one of many MRs opened in order to improve the overall
internationalisation of the GitLab codebase.

i18n documentation
https://docs.gitlab.com/ee/development/i18n/externalization.html

Attempt to debug https://gitlab.com/gitlab-org/gitlab-ce/issues/60953

Fix slow performance with compiling HAML templates

Closes gitlab-ee#11198

See merge request gitlab-org/gitlab-ce!27782

Disallow read user scope to read project events

See merge request gitlab/gitlabhq!3067

In Rails 5, including `ActionView::Context` can have a significant and
hidden performance penalty because this module also includes
`ActionView::CompiledTemplates`. This means that any module that
includes ActionView::Context becomes a descendant of
`CompiledTemplates`.

When a partial is rendered for the first time, it runs
`ActionView::CompiledTemplates#module_eval`, which will evaluate a
string that defines a new method for that partial. For example, the
source of partial might be this string:

```
def _app_views_project_show_html_haml___12345(local_assigns, output)
  "hello world"
end
```

When this string is evaluated, the Ruby interpreter will define the
method and clear the global method cache for all descendants of
`ActionView::CompiledTemplates`. Previous to this change, we
inadvertently made a number of modules fall into this category:

* GroupChildEntity
* NoteUserEntity
* Notify
* MergeRequestUserEntity
* AnalyticsCommitEntity
* CommitEntity
* UserEntity
* Kaminari::Helpers::Paginator
* CurrentUserEntity
* ActionView::Base
* ActionDispatch::DebugExceptions::DebugView
* MarkupHelper
* MergeRequestPresenter

After this change:

* Kaminari::Helpers::Paginator
* ActionView::Base
* ActionDispatch::DebugExceptions::DebugView

Each time a partial is rendered for the first time, all methods for
those modules will have to be redefined. This can exact a significant
performance penalty.

How bad is this penalty? Using the following benchmark script, we can
use DTrace to sample the Ruby interpreter:

```
Benchmark.bm do |x|
  x.report do
    1000.times do
      ActionView::CompiledTemplates.module_eval("def testme\nend")
    end
  end
end
```

This revealed a 11x jump in the time spent in `core#define_method`
alone.

Rails 6 fixes this behavior by moving the `include CompiledTemplates`
into ActionView::Base so that including `ActionView::Context` doesn't
quietly affect other modules in this way.

Closes https://gitlab.com/gitlab-org/gitlab-ee/issues/11198

With Pipelines for Merge Requests feature, users cannout keep using
$CI_COMMIT_REF_NAME and _SLUG predefined variables for dynamic
environments. We fix this problem by explicitly looking at the source
ref.

Fix text based on example

See merge request gitlab-org/gitlab-ce!27787

The reason for the change is that reading the code it should be si-
milar to reading a newspaper, where high-level information is at
the top, like the title and summary of the news, and low level, or
more specific information, are at the bottom.

This improves code readability.

Fix links to wiki pages with subdirectories in search

Closes #56234

See merge request gitlab-org/gitlab-ce!27400

This commit contains the patch suggested by @fjsanpedro in the issue
covering broken links in wiki search results.

Fixes https://gitlab.com/gitlab-org/gitlab-ce/issues/56234

Upgrade CI images to use Chrome V73

See merge request gitlab-org/gitlab-ce!27762

Port changes for design management to CE

See merge request gitlab-org/gitlab-ce!27555

Resolve "Deployment jobs broken as of 11.10.0"

Closes #60821

See merge request gitlab-org/gitlab-ce!27687

Fix GitHub oAuth test

Closes gitlab-org/quality/nightly#98

See merge request gitlab-org/gitlab-ce!27736

Load environment metrics only for JSON endpoint

See merge request gitlab-org/gitlab-ce!27743

When showing the HTML version of the environment metrics we don't need
to fetch their metrics because we don't use them anymore on the HTML
version.

We use additional_metrics.json endpoint now.

Avoid links requiring permissions

Closes #59653

See merge request gitlab-org/gitlab-ce!27797

Init MR Popovers on system note mounted

Closes #60855

See merge request gitlab-org/gitlab-ce!27747

Fix Profiler to work with Rails 5.1

Closes #61051

See merge request gitlab-org/gitlab-ce!27774