`current_application_settings` belongs on `Gitlab::CurrentSettings`

The initializers including this were doing so at the top level, so every object
loaded after them had a `current_application_settings` method. However, if
someone had rack-attack enabled (which was loaded before these initializers), it
would try to load the API, and fail, because `Gitlab::CurrentSettings` didn't
have that method.

To fix this:

1. Don't include `Gitlab::CurrentSettings` at the top level. We do not need
   `Object.new.current_application_settings` to work.
2. Make `Gitlab::CurrentSettings` explicitly `extend self`, as we already use it
   like that in several places.
3. Change the initializers to use that new form.

app/controllers/concerns/requires_whitelisted_monitoring_client.rb

 module RequiresWhitelistedMonitoringClient
   extend ActiveSupport::Concern
+
+  include Gitlab::CurrentSettings
+
   included do
     before_action :validate_ip_whitelisted_or_valid_token!
   end

app/helpers/application_helper.rb

@@ -202,7 +202,7 @@ module ApplicationHelper
   end
   def support_url
-    current_application_settings.help_page_support_url.presence || promo_url + '/getting-help/'
+    Gitlab::CurrentSettings.current_application_settings.help_page_support_url.presence || promo_url + '/getting-help/'
   end
   def page_filter_path(options = {})

app/helpers/application_settings_helper.rb

 module ApplicationSettingsHelper
   extend self
+
+  include Gitlab::CurrentSettings
+
   delegate  :gravatar_enabled?,
             :signup_enabled?,
             :password_authentication_enabled?,

app/helpers/auth_helper.rb

 module AuthHelper
+  include Gitlab::CurrentSettings
+
   PROVIDERS_WITH_ICONS = %w(twitter github gitlab bitbucket google_oauth2 facebook azure_oauth2 authentiq).freeze
   FORM_BASED_PROVIDERS = [/\Aldap/, 'crowd'].freeze

app/helpers/projects_helper.rb

 module ProjectsHelper
+  include Gitlab::CurrentSettings
+
   def link_to_project(project)
     link_to [project.namespace.becomes(Namespace), project], title: h(project.name) do
       title = content_tag(:span, project.name, class: 'project-name')

app/mailers/base_mailer.rb

 class BaseMailer < ActionMailer::Base
+  include Gitlab::CurrentSettings
+
   around_action :render_with_default_locale
   helper ApplicationHelper
   helper MarkupHelper
   attr_accessor :current_user
-  helper_method :current_user, :can?
+  helper_method :current_user, :can?, :current_application_settings
   default from:     proc { default_sender_address.format }
   default reply_to: proc { default_reply_to_address.format }

app/models/concerns/spammable.rb

@@ -28,7 +28,7 @@ module Spammable
   def submittable_as_spam?
     if user_agent_detail
-      user_agent_detail.submittable? && current_application_settings.akismet_enabled
+      user_agent_detail.submittable? && Gitlab::CurrentSettings.current_application_settings.akismet_enabled
     else
       false
     end

app/models/project.rb

@@ -19,6 +19,7 @@ class Project < ActiveRecord::Base
   include Routable
   extend Gitlab::ConfigHelper
+  extend Gitlab::CurrentSettings
   BoardLimitExceeded = Class.new(StandardError)

app/models/protected_branch.rb

@@ -2,6 +2,8 @@ class ProtectedBranch < ActiveRecord::Base
   include Gitlab::ShellAdapter
   include ProtectedRef
+  extend Gitlab::CurrentSettings
+
   protected_ref_access_levels :merge, :push
   # Check if branch name is marked as protected in the system

app/models/snippet.rb

@@ -10,6 +10,8 @@ class Snippet < ActiveRecord::Base
   include Spammable
   include Editable
+  extend Gitlab::CurrentSettings
+
   cache_markdown_field :title, pipeline: :single_line
   cache_markdown_field :description
   cache_markdown_field :content

app/models/user.rb

@@ -2,6 +2,7 @@ require 'carrierwave/orm/activerecord'
 class User < ActiveRecord::Base
   extend Gitlab::ConfigHelper
+  extend Gitlab::CurrentSettings
   include Gitlab::ConfigHelper
   include Gitlab::CurrentSettings

app/policies/base_policy.rb

 require_dependency 'declarative_policy'
 class BasePolicy < DeclarativePolicy::Base
-  include Gitlab::CurrentSettings
-
   desc "User is an instance admin"
   with_options scope: :user, score: 0
   condition(:admin) { @user&.admin? }
@@ -15,6 +13,6 @@ class BasePolicy < DeclarativePolicy::Base
   desc "The application is restricted from public visibility"
   condition(:restricted_public_level, scope: :global) do
-    current_application_settings.restricted_visibility_levels.include?(Gitlab::VisibilityLevel::PUBLIC)
+    Gitlab::CurrentSettings.current_application_settings.restricted_visibility_levels.include?(Gitlab::VisibilityLevel::PUBLIC)
   end
 end

app/services/akismet_service.rb

 class AkismetService
+  include Gitlab::CurrentSettings
+
   attr_accessor :owner, :text, :options
   def initialize(owner, text, options = {})

app/services/auth/container_registry_authentication_service.rb

 module Auth
   class ContainerRegistryAuthenticationService < BaseService
-    include Gitlab::CurrentSettings
+    extend Gitlab::CurrentSettings
     AUDIENCE = 'container_registry'.freeze

app/services/projects/update_pages_service.rb

 module Projects
   class UpdatePagesService < BaseService
+    include Gitlab::CurrentSettings
+
     BLOCK_SIZE = 32.kilobytes
     MAX_SIZE = 1.terabyte
     SITE_PATH = 'public/'.freeze

app/services/upload_service.rb

 class UploadService
+  include Gitlab::CurrentSettings
+
   def initialize(model, file, uploader_class = FileUploader)
     @model, @file, @uploader_class = model, file, uploader_class
   end

app/services/users/build_service.rb

 module Users
   class BuildService < BaseService
+    include Gitlab::CurrentSettings
+
     def initialize(current_user, params = {})
       @current_user = current_user
       @params = params.dup

config/initializers/sentry.rb

 # Be sure to restart your server when you modify this file.
 require 'gitlab/current_settings'
-include Gitlab::CurrentSettings
 if Rails.env.production?
   # allow it to fail: it may do so when create_from_defaults is executed before migrations are actually done
   begin
-    sentry_enabled = current_application_settings.sentry_enabled
+    sentry_enabled = Gitlab::CurrentSettings.current_application_settings.sentry_enabled
   rescue
     sentry_enabled = false
   end
   if sentry_enabled
     Raven.configure do |config|
-      config.dsn = current_application_settings.sentry_dsn
+      config.dsn = Gitlab::CurrentSettings.current_application_settings.sentry_dsn
       config.release = Gitlab::REVISION
       # Sanitize fields based on those sanitized from Rails.

config/initializers/session_store.rb

 # Be sure to restart your server when you modify this file.
 require 'gitlab/current_settings'
-include Gitlab::CurrentSettings
 # allow it to fail: it may do so when create_from_defaults is executed before migrations are actually done
 begin
-  Settings.gitlab['session_expire_delay'] = current_application_settings.session_expire_delay || 10080
+  Settings.gitlab['session_expire_delay'] = Gitlab::CurrentSettings.current_application_settings.session_expire_delay || 10080
 rescue
   Settings.gitlab['session_expire_delay'] ||= 10080
 end

lib/api/helpers/runner.rb

 module API
   module Helpers
     module Runner
+      include Gitlab::CurrentSettings
+
       JOB_TOKEN_HEADER = 'HTTP_JOB_TOKEN'.freeze
       JOB_TOKEN_PARAM = :token
       UPDATE_RUNNER_EVERY = 10 * 60