This backports changes made in
https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/9134.

Moves shared code into a mixin

See merge request gitlab-org/gitlab-ce!24322

Add Import/Export dev docs

Closes #36055

See merge request gitlab-org/gitlab-ce!23835

GitLab 11.4.3 "Outbound requests" setting path

See merge request gitlab-org/gitlab-ce!22898

Fix no avatar not showing in user selection box

Closes #56268

See merge request gitlab-org/gitlab-ce!24346

Add 11.7 -> 11.8 update doc

See merge request gitlab-org/gitlab-ce!24283

Resolve "Add "What's new" menu item in top navigation"

Closes #25341

See merge request gitlab-org/gitlab-ce!23186

Fix Bitbucket Server importer error handling

Closes #56154

See merge request gitlab-org/gitlab-ce!24343

Ensure pool participants are linked before GC

Closes gitaly#1354

See merge request gitlab-org/gitlab-ce!24230

Bump minimal node version from 6 to 8.10.0

Closes #54065

See merge request gitlab-org/gitlab-ce!24305

Update Gitaly documentation to indicate which version shipped with Gitaly TLS support

See merge request gitlab-org/gitlab-ce!24334

In theory the case could happen that the initial linking of the pool
fails and so do all the retries that Sidekiq performs. This could lead
to data loss.

To prevent that case, linking is done before Gits GC too. This makes
sure that case doesn't happen.

Adjust applied suggestion reverting previous changes

Closes #56017

See merge request gitlab-org/gitlab-ce!24250

Fix broken MR coach link

See merge request gitlab-org/gitlab-ce!24327

Resolve "undefined method `count_of_extra_tags_not_shown'"

Closes #56311

See merge request gitlab-org/gitlab-ce!24354

Fixes several ActionController::Parameters deprecations

See merge request gitlab-org/gitlab-ce!24332

Bump kubectl in Auto DevOps to 1.11.6

See merge request gitlab-org/gitlab-ce!24176

Bump nginx-ingress chart to 1.1.2

See merge request gitlab-org/gitlab-ce!24203

web-terminal: Add support for URL to Link parsing

See merge request gitlab-org/gitlab-ce!24242

- Add tests for project topics

Update gitlab-styles to 2.5.1

See merge request gitlab-org/gitlab-ce!24336

Move job cancel button

Closes #55944 and #54812

See merge request gitlab-org/gitlab-ce!24074

Rename Add style proposal

See merge request gitlab-org/gitlab-ce!24353

Docs: Update link title, we support more than GKE

See merge request gitlab-org/gitlab-ce!24347

Refactor the API OAuth docs

See merge request gitlab-org/gitlab-ce!24295

Documentation: In Project Members page, add serial comma

See merge request gitlab-org/gitlab-ce!24348

Fix indentation and markup for Markdown codeblock

See merge request gitlab-org/gitlab-ce!24321

docs: emoji cheat sheet with shortcodes

Closes #42672

See merge request gitlab-org/gitlab-ce!24320

After upgrading to Ruby 2.5.3, we switched `URI.join` in favor of
`Gitlab::Utils.append_path`. However,
ActionController::Base.helpers.image_path can return a full URL if a CDN
host is present.

Rails provides a way to generate the full URL using the asset path, but
that doesn't appear to work because `request` is nil`.

Revert to the previous behavior to handle CDNs and relative URLs.

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/56268