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.

spec/requests/sidebar_sections_controller_spec.rb

@@ -4,14 +4,6 @@ RSpec.describe SidebarSectionsController do
   fab!(:user) { Fabricate(:user) }
   fab!(:admin) { Fabricate(:admin) }
 
-  before do
-    ### TODO remove when enable_custom_sidebar_sections SiteSetting is removed
-    group = Fabricate(:group)
-    Fabricate(:group_user, group: group, user: user)
-    Fabricate(:group_user, group: group, user: admin)
-    SiteSetting.enable_custom_sidebar_sections = group.id.to_s
-  end
-
   describe "#index" do
     fab!(:sidebar_section) { Fabricate(:sidebar_section, title: "private section", user: user) }
     fab!(:sidebar_url_1) { Fabricate(:sidebar_url, name: "tags", value: "/tags") }
@@ -29,7 +21,7 @@ RSpec.describe SidebarSectionsController do
       get "/sidebar_sections.json"
       expect(response.status).to eq(200)
       expect(response.parsed_body["sidebar_sections"].map { |section| section["title"] }).to eq(
-        ["public section", "private section"],
+        ["Community", "public section", "private section"],
       )
     end
   end
@@ -49,6 +41,8 @@ RSpec.describe SidebarSectionsController do
 
     it "creates custom section for user" do
       sign_in(user)
+      expect(SidebarSection.count).to eq(1)
+
       post "/sidebar_sections.json",
            params: {
              title: "custom section",
@@ -66,7 +60,7 @@ RSpec.describe SidebarSectionsController do
 
       expect(response.status).to eq(200)
 
-      expect(SidebarSection.count).to eq(1)
+      expect(SidebarSection.count).to eq(2)
       sidebar_section = SidebarSection.last
 
       expect(sidebar_section.title).to eq("custom section")