Add rake task to load sdg

This task should be useful for existing installations that are going
to upgrade the app and want to load SDG data into an already
existing database.

lib/tasks/db.rake

@@ -4,4 +4,10 @@ namespace :db do
     @avoid_log = args[:print_log] == "avoid_log"
     load(Rails.root.join("db", "dev_seeds.rb"))
   end
+
+  desc "Load SDG content into database"
+  task load_sdg: :environment do
+    ApplicationLogger.new.info "Adding Sustainable Development Goals content"
+    load(Rails.root.join("db", "sdg.rb"))
+  end
 end