Add retention policy for cached content and media (#19232)

spec/fabricators/access_grant_fabricator.rb

@@ -0,0 +1,6 @@
+Fabricator :access_grant, from: 'Doorkeeper::AccessGrant' do
+  application
+  resource_owner_id { Fabricate(:user).id }
+  expires_in 3_600
+  redirect_uri { Doorkeeper.configuration.native_redirect_uri }
+end

spec/fabricators/preview_card_fabricator.rb

@@ -3,4 +3,5 @@ Fabricator(:preview_card) do
   title { Faker::Lorem.sentence }
   description { Faker::Lorem.paragraph }
   type 'link'
+  image { attachment_fixture('attachment.jpg') }
 end