The `ProjectPolicy` is meant to be declarative in nature, and it isn't
necessarily a good idea to remove all duplication here. That level of
indirection would _hurt_ readability, rather than improve it.

1. Extract an `admin_or_auditor?` method to clean up multiple uses of
  `user.admin? || user.auditor?`

2. Follow the four phase test rule.

3. Clean up the `project_policy_spec` by using %i for literal symbols

4. A number of other minor improvements.

Don't repeat declarations that are common between anonymous and auditor users.

All finders, policies and controllers that needed to be modified to include an
`auditor` check are tested here

In addition, allow an auditor read-only permissions within a project.

  Collect all the permissions that an auditor is supposed to have in the
  `auditor_access` method. This _could_ be automated by dynamically listing all
  permissions that start with `read_`, but this is cleaner / more readable,
  especially since it's confined to this one location.

An auditor user is intended to be user with read-only access to all projects and
groups. Access to the admin area and any project settings pages are disallowed

This commit lays the initial groundwork for this concept - adding an `auditor`
column to the `users` table, as well as a few supplements.

Port "V4 API: Remove deprecated MR and Issue endpoints and preserve V3 namespace"

See merge request !1166

Geo: send the new event type with the backfill function

Closes #1645

See merge request !1157

CE upstream

Closes gitlab-ce#27674

See merge request !1170

CE upstream

Closes #395

See merge request !1161

Add index to labels for `type` and project_id`

Closes #27676

See merge request !8978

Fixed typo in slash commands docs

Closes #27674

See merge request !8976

Fix "NameError: uninitialized constant Rack::Proxy" in production environment

See merge request !1168

When loading pages that display the number of open issues,
the backend runs a query such as:

```sql
SELECT "labels"."id" FROM "labels" WHERE "labels"."type" IN ('ProjectLabel') AND "labels"."project_id" = 1000
```

This results in an entire scan of the `labels` table. To optimize performance,
add the appropriate index to the table.

Closes #27676

Fix "NameError: uninitialized constant Rack::Proxy" in production environment

See merge request !8977

Fixes gitlab-org/gitlab-ce#27674

UX Guide: Button placement in groups

See merge request !8972

Integrate webpack for frontend asset compilation

Closes #14634

See merge request !7288

Port "Integrate webpack for frontend asset compilation" to EE

See merge request !1138

* master: (54 commits)
  Move project services to new location under Integrations
  Move webhooks to new a location under Integrations
  Fix documentation link in doc/user/project/pages/index.md
  Fixed merge request widget tests
  Small documentation changes and fixes for Geo
  Remove ‘EE-specific’ comments related to Pages feature
  Update specs with new method signatures
  rm_tag now takes a user argument
  Use GitOperationService instead
  Merge remote-tracking branch 'ce/fix-git-hooks-when-creating-file' into master-ce
  Mentioned pages to CE port in project/pages/index.md
  Fixed merge request environment not displaying
  Update guidance on handling shared secrets in HA setup
  Pull EE specific Gitlab::Auth code in to its own module
  Use `add_$role` helper in snippets specs
  Check public snippets for spam
  Keep snippet visibility on error
  Add info on using both push/pull repository mirroring
  Properly read approvalPending from dataset.
  Fix data attr spacing.
  ...