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

i18n JS files starting with i - EE

See merge request gitlab-org/gitlab-ee!12454

Resolve CE/EE diffs in accounts/show

Closes #11046

See merge request gitlab-org/gitlab-ee!12733

Resolve CE/EE diffs in help/index

Closes gitlab-ee#11051

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

Resolve CE/EE diffs in help/index

Closes #11051

See merge request gitlab-org/gitlab-ee!12728

Resolve CE/EE diffs in signup_box

Closes gitlab-ee#11047

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

Resolve CE/EE diffs in signup_box

Closes #11047

See merge request gitlab-org/gitlab-ee!12730

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 Clusters::Instance invocation scope

See merge request gitlab-org/gitlab-ee!12740

Use `::Clusters::Instance` instead of just `Clusters::Instance` so that
this works in development too (there is also `EE::Clusters`).

Fix loadJSONFixtures wrapper in Jest

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

Merge branch '11566-do-not-fetch-all-public-groups-for-approval-rule-when-search-is-empty' into 'master'

Resolve "Do not fetch all public groups for approval rule when search is empty"

Closes #11566

See merge request gitlab-org/gitlab-ee!12628

Mock away document.createRange() in Jest

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

Move security dashboard filter test to Jest

See merge request gitlab-org/gitlab-ee!12518

i18n JS files starting with n

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

i18n JS files starting with n - EE

See merge request gitlab-org/gitlab-ee!12412

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

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

Fix flyout nav on small viewports

Closes gitlab-ce#58727

See merge request gitlab-org/gitlab-ee!9961

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