DEV: move sidebar community section to database (#21166)

* DEV: move sidebar community section to database

Before, community section was hard-coded. In the future, we are planning to allow admins to edit it. Therefore, it has to be moved to database to `custom_sections` table.

Few steps and simplifications has to be made:
- custom section was hidden behind `enable_custom_sidebar_sections` feature flag. It has to be deleted so all forums, see community section;
- migration to add `section_type` column to sidebar section to show it is a special type;
- migration to add `segment` column to sidebar links to determine if link should be displayed in primary section or in more section;
- simplify more section to have one level only (secondary section links are merged);
- ensure that links like `everything` are correctly tracking state;
- make user an anonymous links position consistence. For example, from now on `faq` link for user and anonymous is visible in more tab;
- delete old community-section template.

app/serializers/current_user_serializer.rb

@@ -69,7 +69,6 @@ class CurrentUserSerializer < BasicUserSerializer
              :sidebar_category_ids,
              :sidebar_list_destination,
              :sidebar_sections,
-             :custom_sidebar_sections_enabled,
              :new_new_view_enabled?
 
   delegate :user_stat, to: :object, private: true
@@ -82,7 +81,7 @@ class CurrentUserSerializer < BasicUserSerializer
       .public_sections
       .or(SidebarSection.where(user_id: object.id))
       .includes(sidebar_section_links: :linkable)
-      .order("(public IS TRUE) DESC")
+      .order("(section_type IS NOT NULL) DESC, (public IS TRUE) DESC")
       .map { |section| SidebarSectionSerializer.new(section, root: false) }
   end
 
@@ -301,12 +300,4 @@ class CurrentUserSerializer < BasicUserSerializer
   def include_new_personal_messages_notifications_count?
     redesigned_user_menu_enabled
   end
-
-  def custom_sidebar_sections_enabled
-    if SiteSetting.enable_custom_sidebar_sections.present?
-      object.in_any_groups?(SiteSetting.enable_custom_sidebar_sections_map)
-    else
-      false
-    end
-  end
 end

app/serializers/sidebar_section_serializer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class SidebarSectionSerializer < ApplicationSerializer
-  attributes :id, :title, :links, :slug, :public
+  attributes :id, :title, :links, :slug, :public, :section_type
 
   def links
     object.sidebar_section_links.map { |link| SidebarUrlSerializer.new(link.linkable, root: false) }

app/serializers/sidebar_url_serializer.rb

@@ -1,7 +1,7 @@
 # frozen_string_literal: true
 
 class SidebarUrlSerializer < ApplicationSerializer
-  attributes :id, :name, :value, :icon, :external
+  attributes :id, :name, :value, :icon, :external, :segment
 
   def external
     object.external? || object.full_reload?

app/serializers/site_serializer.rb

@@ -266,6 +266,7 @@ class SiteSerializer < ApplicationSerializer
     SidebarSection
       .public_sections
       .includes(sidebar_section_links: :linkable)
+      .order("(section_type IS NOT NULL) DESC, (public IS TRUE) DESC")
       .map { |section| SidebarSectionSerializer.new(section, root: false) }
   end