Fixes issues with show whitespace button in diffs

Closes #42597 and #58852

See merge request gitlab-org/gitlab-ce!28242

Add Let's Encrypt client

See merge request gitlab-org/gitlab-ce!27624

Part of adding Let's Encrypt certificates for pages domains

Add acme-client gem

Client is being initialized by private key stored in secrets.yml
Let's Encrypt account is being created lazily.
If it's already created, Acme::Client just gets account_kid by
calling new_account method

Make Let's Encrypt client an instance
Wrap order and challenge classes

Properly clear the merge error upon rebase failure

Closes #56139

See merge request gitlab-org/gitlab-ce!28319

i18n JS files starting with i

See merge request gitlab-org/gitlab-ce!28010

Resolve CE/EE diffs in help/index

Closes gitlab-ee#11051

See merge request gitlab-org/gitlab-ce!28335

Resolve CE/EE diffs in signup_box

Closes gitlab-ee#11047

See merge request gitlab-org/gitlab-ce!28336

If `merge_error` is ever set after a failure, it is never cleared, even
after a subsequent, successful rebase. We now clear this field whenever
a successful rebase occurs.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56139

clarify that "team" means "project" when considered for assignment purposes.

See merge request gitlab-org/gitlab-ce!27753

Add info about the single docs codebase effort

See merge request gitlab-org/gitlab-ce!28127

Fix loadJSONFixtures wrapper in Jest

See merge request gitlab-org/gitlab-ce!28328

Mock away document.createRange() in Jest

See merge request gitlab-org/gitlab-ce!28222

i18n JS files starting with n

See merge request gitlab-org/gitlab-ce!28132

Merge branch 'ce-quick-fix-58727-collapsed-sidebar-flyout-menu-items-don-t-appear-in-1200px-screen-size' into 'master'

CE Fix flyout nav on small viewports

See merge request gitlab-org/gitlab-ce!25998

Sessions can be listed for a given user

See merge request gitlab-org/gitlab-ce!28306

Suppress keychain access popup from chromedriver in Karma

See merge request gitlab-org/gitlab-ce!28310

Docs: couple of improvements to the Vuex frontend guide

See merge request gitlab-org/gitlab-ce!28257

Update mysql.md: variables values should be quoted, otherwise you get an...

See merge request gitlab-org/gitlab-ce!24214

Update mysql.md: variables values should be quoted, otherwise you get an "variables config should be a hash of key value pairs" error

[CI doc] Add chat value to only keyword

See merge request gitlab-org/gitlab-ce!27417

recursive/nested includes supported now

See merge request gitlab-org/gitlab-ce!28155

upgrate example ymal file, change type to stage.

See merge request gitlab-org/gitlab-ce!27992

docs: improve architecture component details

See merge request gitlab-org/gitlab-ce!28280

Docs: Add premium & silver badge to group project templates docs

Closes gitlab-ee#11587

See merge request gitlab-org/gitlab-ce!28304

Docs: update link to new security docs

See merge request gitlab-org/gitlab-ce!28299

docs: use sudo on gitlab-rake gitlab:features:*

See merge request gitlab-org/gitlab-ce!28288

Fix a typo mentioning SAST instead of DAST

See merge request gitlab-org/gitlab-ce!28308

Fix ES indexer install script - remove leading /

See merge request gitlab-org/gitlab-ce!28231

Fix typo in index.md

See merge request gitlab-org/gitlab-ce!28311

Removed the unnecessary line. It would be covered anyway by line 352...

See merge request gitlab-org/gitlab-ce!28228

Rjh/doc fixes for source install

See merge request gitlab-org/gitlab-ce!27916

Adds developer documentation for accessing session data in GitLab

See merge request gitlab-org/gitlab-ce!27996

Part of single codebase changes.

An instance of i18n which required sprintf was not handled correctly
and has been fixed in this commit.

Further to this, i18n was applied to
  app/assets/javascripts/new_branch_form.js
but needed to be removed as the i18n was too vague.

A note has been made to follow up on this file.

Part of single codebase changes.