Set Referrer-Policy to origin in web UI and public pages of private toots (#7162)

Fix #7115

app/controllers/home_controller.rb

@@ -2,6 +2,7 @@
 
 class HomeController < ApplicationController
   before_action :authenticate_user!
+  before_action :set_referrer_policy_header
   before_action :set_initial_state_json
 
   def index
@@ -62,4 +63,8 @@ class HomeController < ApplicationController
       about_path
     end
   end
+
+  def set_referrer_policy_header
+    response.headers['Referrer-Policy'] = 'origin'
+  end
 end