Docs: Bring HTML Style Guide in line with docs standards

See merge request gitlab-org/gitlab-ce!26252

Collapse diff tree is only one file is present

Closes #53139

See merge request gitlab-org/gitlab-ce!26280

Closes https://gitlab.com/gitlab-org/gitlab-ce/issues/53139

Merge the gitlab-shell "gitlab-keys" functionality into GitLab CE

Closes #56089

See merge request gitlab-org/gitlab-ce!25598

In this commit, some methods that aren't being used
are removed from `Gitlab::Shell`. They are the ff:
- `#remove_keys_not_found_in_db`
- `#batch_read_key_ids`
- `#list_key_ids`

The corresponding methods in `Gitlab::Keys` have been
removed as well.

Revert "New Repository#insights_config method"

See merge request gitlab-org/gitlab-ce!26315

Add users search results to global search

Closes #25973

See merge request gitlab-org/gitlab-ce!21197

Remove diff tree filtering feature flag

See merge request gitlab-org/gitlab-ce!26273

Make runners token encryption to be optional

See merge request gitlab-org/gitlab-ce!26223

This reverts merge request !26183

Bump Rugged to 0.28.0

See merge request gitlab-org/gitlab-ce!25660

Remove before_script from DAST vendored template

See merge request gitlab-org/gitlab-ce!26281

Link to the gitaly repository's Beginniner's Guide documentation

See merge request gitlab-org/gitlab-ce!25627

Copyedit pipelines-related documentation

Closes #59006

See merge request gitlab-org/gitlab-ce!26198

Refactor new content for stage keyword

See merge request gitlab-org/gitlab-ce!25953

Add registry to dev arch docs

See merge request gitlab-org/gitlab-ce!25951

Add registry to dev arch docs

See merge request gitlab-org/gitlab-ce!25951

This version bump makes things consistent between Gitaly and
fixes a significant number of bugs:
https://github.com/libgit2/libgit2/releases

This also decreases disk space of Omnibus builds by ~30 MB.

There is also a workaround for
https://github.com/libgit2/rugged/issues/785. If Gitaly or another
process changes .gitconfig while Rugged has the file loaded,
Rugged::Repository#each_key will report stale values unless a lookup is
done first.

This bug only manifests in a spec because we are using both Gitaly and
Rugged at the same time there, and we normally don't use Rugged in the
CE/EE code in this way.

Merge branch '47491-gitlab-fakeapplicationsettings-doesn-t-respond-to-all-the-methods-applicationsetting-responds-to-itself' into 'master'

Introduce ApplicationSettingImplementation

Closes #47491

See merge request gitlab-org/gitlab-ce!25803

Add artillery.io load testing script and rake tasks

See merge request gitlab-org/gitlab-ce!26210

Also add rake tasks that makes use of existing performance data
genertion task.

So the fake can enjoy it, too. We don't use `prepend`
because that'll require we change `allow_any_instance_of` to
`expect_next_instance_of`, but that's not very easy to do.
We can do that later.

Fix undefined variable error on json project views

See merge request gitlab-org/gitlab-ce!26297

This mistake seems to have always been there, but it only resulted in
errors on the `/explore*.json` since they were the one that _actually_
relied on the local variables.

Fix spec for routes to the GraphqlController

See merge request gitlab-org/gitlab-ce!26231

Implement suggestion diff lines parser

See merge request gitlab-org/gitlab-ce!26069

Fix test-plan label in the template

See merge request gitlab-org/gitlab-ce!26283

Fixed backup of non default upload directory

See merge request gitlab-org/gitlab-ce!25736

Replaced Settings with Gitlab.config for uniformity