The new service takes stages order into account.

Reason for renaming is to comply with naming convention of services in
codebase.

* Changed name of delete_user_service and worker to destroy
* Move and change delete_group_service to Groups::DestroyService
* Rename Notes::DeleteService to Notes::DestroyService

This ensures that project authorizations are refreshed when moving a
project from one namespace to another. When doing so the permissions for
all users of both the old and new namespaces are refreshed.

See #26194 for more information.

Allows to use slash command /target_branch <target_branch_name> in merge requests notes and description.
Command allows to specify target branch for current merge request.

Proposed in #23619

Backport changes from the EE-only squash implementation, which would
otherwise conflict when merge CE into EE.

<https://gitlab.com/gitlab-org/gitlab-ee/merge_requests/1024>

add complete changelog for !8949

Apply the same spam checks to public snippets (either personal snippets
that are public, or public snippets on public projects) as to issues on
public projects.

There is now a `Projects::Settings` module, for the members
controller. Ensure that we get the actual settings, not that module.

Due to autoloading and Ruby scoping, the .update file was never being
updated due to this error:

```
NoMethodError: undefined method `pages' for Projects::Settings:Module
        from /opt/gitlab/embedded/service/gitlab-rails/app/services/projects/update_pages_configuration_service.rb:50:in `pages_update_file'
        from /opt/gitlab/embedded/service/gitlab-rails/lib/gitlab/metrics/instrumentation.rb:157:in `pages_update_file'
        from (irb):6
        from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.7.1/lib/rails/commands/console.rb:110:in `start'
        from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.7.1/lib/rails/commands/console.rb:9:in `start'
        from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.7.1/lib/rails/commands/commands_tasks.rb:68:in `console'
        from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.7.1/lib/rails/commands/commands_tasks.rb:39:in `run_command!'
        from /opt/gitlab/embedded/lib/ruby/gems/2.3.0/gems/railties-4.2.7.1/lib/rails/commands.rb:17:in `<top (required)>'
        from bin/rails:9:in `require'
```

This error was caught and discarded quietly. This fix exercises this code and fixes the scope problem.

Closes gitlab-com/infrastructure#1058

The ZIP archive size is calculated from artifacts metadata that should get uploaded for new artifacts

- Move UploadsTransfer to ProjectTransfer and inherit from this to UploadsTransfer and PagesTransfer

- The pages are created when build artifacts for `pages` job are uploaded
- Pages serve the content under: http://group.pages.domain.com/project
- Pages can be used to serve the group page, special project named as host: group.pages.domain.com
- User can provide own 403 and 404 error pages by creating 403.html and 404.html in group page project
- Pages can be explicitly removed from the project by clicking Remove Pages in Project Settings
- The size of pages is limited by Application Setting: max pages size, which limits the maximum size of unpacked archive (default: 100MB)
- The public/ is extracted from artifacts and content is served as static pages
- Pages asynchronous worker use `dd` to limit the unpacked tar size
- Pages needs to be explicitly enabled and domain needs to be specified in gitlab.yml
- Pages are part of backups
- Pages notify the deployment status using Commit Status API
- Pages use a new sidekiq queue: pages
- Pages use a separate nginx config which needs to be explicitly added

Fixes #24021

add changelog entry

replace local variables `merge_request` with instance ones

modify `MergeRequests::BuildService` to fix failed tests

extract `assign_target_project` method

remove unnecessary instance variables

remove exclamation marks and rewrite conditionals to improve readability

extract `params_does_not_contain_branches?` method, rename `unprepared_merge_request` method to `uncreatable_merge_request`

replace instance variables `merge_request` and `error_messages` with getters and setters; divide `set_title_and_description` method on two separate ones

refactor `execute` method

return `set_title_and_description` method

rename `branches_selected?` method to `branches_present?` to make it more different from `branches_specified?`

fixes after discussion

renamed method branches_valid?

fix space

return assigning methods into `execute` method

simplify `find_target_branch` and `find_source_project` methods

fix spec `merge request issuable record that supports slash commands in its description and notes`