Allow all snippets to be accessed by API

Closes #41888

See merge request gitlab-org/gitlab-ce!25772

Fix exports related to new templates

Closes #58570

See merge request gitlab-org/gitlab-ce!25794

This reverts commit 669d84356771682961ac6c416c3cbdb983ec0cd2

Fix typo in review-performance job

See merge request gitlab-org/gitlab-ce!25821

This reverts commit 9f7dd413, reversing
changes made to 663d2e43.

This reverts commit c9ecc71a, reversing
changes made to c3c8dbf8.

Adds Rubocop ReturnNil cop

Closes #57454

See merge request gitlab-org/gitlab-ce!25034

Adds the Rubocop ReturnNil cop

Closes gitlab-ce#57454

See merge request gitlab-org/gitlab-ee!9867

Quarantine failing ssh key tests

See merge request gitlab-org/gitlab-ee!9883

Allow GraphQL requests without CSRF token

Closes #57237

See merge request gitlab-org/gitlab-ce!25719

Document ChatOps for actor feature gates

See merge request gitlab-org/gitlab-ce!25815

Quarantine CI variable support spec

See merge request gitlab-org/gitlab-ee!9882

Quarantine failing ssh key test

See merge request gitlab-org/gitlab-ce!25813

This style change enforces `return if ...` instead of
`return nil if ...` to save maintainers a few minor review points.

Style change discussed in
https://gitlab.com/gitlab-org/gitlab-ce/issues/57454

Quarantine: Update failure issue link

See merge request gitlab-org/gitlab-ce!25811

This style change enforces `return if ...` instead of
`return nil if ...` to save maintainers a few minor review points

The documentations only covered the percentage based feature gates.
These don't work really well for a number of reasons, for example; a new
visual element in GitLab would be weird to see only 25% of the time.

Allowing feature gates based on projects and groups has been supported,
now it's documented.

CE backport of ee-parallel-diff-view

See merge request gitlab-org/gitlab-ce!25734

Fix EE differences in parallel_diff_view.vue

Closes #10007

See merge request gitlab-org/gitlab-ee!9825

With this we allow authentication using a session or using personal
access token.

Authentication using a session, and CSRF token makes it easy to play
with GraphQL from the Graphiql endpoint we expose.

But we cannot enforce CSRF validity, otherwise authentication for
regular API clients would fail when they use personal access tokens to
authenticate.

Re-add gitlab:ui:visual ci job

Closes gitlab-ui#192

See merge request gitlab-org/gitlab-ce!25808

These adjustments make sure our GraphQL helpers support rendering
queries for empty fields like this:

      {
        echo(text: "Hello world")
      }

Instead of like this:

     {
       echo(text: "Hello world") {
       }
     }

The latter would be an invalid query, causing parsing errors.

Making review-performance run on master in scheduled runs

Closes #57881

See merge request gitlab-org/gitlab-ce!25757