This adds validations that ensure that wiki pages cannot have the same
canonical slug in the same project. We cannot easily move this check to
the DB, so this is handled in logic - we check in `.find_or_create` if
either of the known slugs matches a record, and we raise errors on
conflict.

This also introduces some optimisations that eliminate unnecessary
queries.

Minor updates from review comments

Includes:

- Use Class#name instead of constant
- Wrap mutable state in an outer transaction

  The one subtle thing here is that the first query (to find the record)
  must be within the transaction, even though it does not mutate the state
  of the DB. This is because we learn important facts from that query
  (namely whether there are any conflicting canonical slugs) that could be
  invalidated outside a transaction.

- Use standard uniqueness validator

  This is more declarative than our hand-rolled implementation

- Move page construction into factory

  This requires a new trait for the wiki page factory to create pages that
  are in the wiki repo.

- Changes to some test descriptions

- Reduce DB queries in specs

we don't strictly need multiple slugs here - one will do.

- Avoid running validation if there is no project_id

- Raise error if there are no slugs at all

Add support for wiki page events

* Update visibility test
* Update action name for wiki page events
* Update event specs to use wiki metadata models
* Add specific factories

This adds a `Policy` for WikiPage::Meta, which is required for
interoperation with `Event#visible_to`. The policy is very simple
- just delegating to the project.

Adds wiki page slug model:

A slug represents a historical set of slugs that identify wiki pages. At
most one can be canonical at any one time, per page.

Adds wiki page meta model:

The wiki page metadata model contains the current title, and has access
to a collection of slugs, at most one of which may be canonical at any
one point (all others are historic).

Rather than polluting the model namespace, and to clarify the meaning of
the class names, these classes are placed under the `WikiPage`
namespace.

Adds adds wiki page meta/spec factories with sequences for use in the
specs, guaranteeing unique titles and slugs

Exposes `@user` as `user`, so that the current page author can be
identified.

Change equality to match other DB objects: pages with equal slugs are
equal.

This adds two new tables, `wiki_page_slugs` and `wiki_page_meta` to hold
metadata about wiki pages.

The string limit for titles is set at our application limit, and the
slug limit is set at the maximum valid URL length.

The rule that one slug at a time may be canonical for a given page is
enforced using a unique index.

Adds changelog describing this change.

Move edition tests to model where they belong

See merge request gitlab-org/gitlab!27362

Revert "Merge branch '31034-enable-zeitwerk' into 'master'"

See merge request gitlab-org/gitlab!27539

Remove feature flag cross_project_need_artifacts

See merge request gitlab-org/gitlab!27404

Fix Gatsby project template

See merge request gitlab-org/gitlab!27538

Count total amount of users for each access level

See merge request gitlab-org/gitlab!25360

Adds metric to derive user creation count

See merge request gitlab-org/gitlab!27351

Resolve "Customizable value stream analytics needs documentation"

Closes #211601

See merge request gitlab-org/gitlab!27497

This commit adds user documentation for the customizable value stream
analytics feature.

Service validation for project and type uniqueness

Closes #207385

See merge request gitlab-org/gitlab!26308

This validation prevents duplicated services of the
same type in the same project. The validation can
only run on create because it is possible that the
database holds invalid data. If this is the case,
updating a service would fail.

Merge branch '211453-value-stream-analytics-top-labels-causing-error-when-tasks_by_type_chart-feature-flag-not' into 'master'

Value stream analytics - top labels causing error when tasks_by_type_chart feature flag not enabled

Closes #211453

See merge request gitlab-org/gitlab!27478

Use bash for bin/background_scripts

See merge request gitlab-org/gitlab!27534

This reverts merge request !20521

The file was missing a VERSION file and project.json, so it was
failing to import.

Possible fix for https://gitlab.com/gitlab-org/gitlab/-/issues/31589

Replace underscore/lodash in design_management

Closes #210260

See merge request gitlab-org/gitlab!27248

The bin/background_jobs_sk_cluster script use some
bashisms. In order to avoid issues with either GDK
or other systems, here we make use of bash as the
default interpreter.

Enable RSpec/LeakyConstantDeclaration cop

See merge request gitlab-org/gitlab!27368

This replaces all underscore usage for lodash inside
the EE feature design_management

Make rspec:coverage only download the artifacts it needs

Closes #211647

See merge request gitlab-org/gitlab!27493

Add doc requirement for API development

See merge request gitlab-org/gitlab!27383

Signed-off-by: Dmitriy Zaporozhets <dmitriy.zaporozhets@gmail.com>

Fix typo in offline appsec docs

See merge request gitlab-org/gitlab!27453

Threat monitoring docs

Closes #211395

See merge request gitlab-org/gitlab!26025

Docs: update predefined variables usage

See merge request gitlab-org/gitlab!27435

Disable correct lint rule

Closes #211681

See merge request gitlab-org/gitlab!27521

OKR: Improve the Markdown page (part 1)

Closes #20612, #24731, and gitlab-docs#652

See merge request gitlab-org/gitlab!26663

- Add docs on the Wiki TOC
- Enhance inline diff section
- Make headings sentence case
- Markdown page Vale style fixes
- Update TOC image name
- Add example to footnote bug
- Write emoji as lowercase

Resolve "CODEOWNERS should enforce reviews for renaming of files"

Closes #198061

See merge request gitlab-org/gitlab!26513

Refactor AuditLogFinder public interface

See merge request gitlab-org/gitlab!27209

This concern should belong to the model. It is also consistent with
patterns across other models (e.g. Issues, MergeRequests)

GraphQL: Upgrade to GraphQL-Ruby 1.10

Closes #207278

See merge request gitlab-org/gitlab!26096