Refactor Cache-Control and Vary definitions (#24347)

app/controllers/relationships_controller.rb

@@ -7,6 +7,7 @@ class RelationshipsController < ApplicationController
   before_action :set_accounts, only: :show
   before_action :set_relationships, only: :show
   before_action :set_body_classes
+  before_action :set_cache_headers
 
   helper_method :following_relationship?, :followed_by_relationship?, :mutual_relationship?
 
@@ -70,4 +71,8 @@ class RelationshipsController < ApplicationController
   def set_body_classes
     @body_classes = 'admin'
   end
+
+  def set_cache_headers
+    response.cache_control.replace(private: true, no_store: true)
+  end
 end