Extract method to provide a title for SDG pages

This way we'll avoid the duplication that can be found in the admin
section.

app/components/sdg_management/goals/index_component.html.erb

@@ -1,8 +1,4 @@
-<% provide(:title) do %>
-  <%= t("sdg_management.header.title") %> - <%= title %>
-<% end %>
-
-<h2><%= title %></h2>
+<%= header %>
 
 <table>
   <thead>

app/components/sdg_management/goals/index_component.rb

@@ -1,4 +1,6 @@
 class SDGManagement::Goals::IndexComponent < ApplicationComponent
+  include SDGManagement::Header
+
   attr_reader :goals
 
   def initialize(goals)

app/components/sdg_management/header.rb

@@ -0,0 +1,11 @@
+module SDGManagement::Header
+  extend ActiveSupport::Concern
+
+  def header
+    provide(:title) do
+      "#{t("sdg_management.header.title")} - #{title}"
+    end
+
+    tag.h2 title
+  end
+end