FEATURE: Use group based setting for unsafe-none COOP (#27783)

Followup 3ff7ce78e782c7d28c8b5a1a3f40a1de897d89a1

Basing this setting on referrer was too brittle --
the referrer header can easily be ommitted or changed.
Instead, for the small amount of use cases that this
site setting serves, we can use a group-based setting
instead, changing it to `cross_origin_opener_unsafe_none_groups`
instead.

db/migrate/20240709010639_remove_cross_origin_unsafe_none_referrers_setting.rb

@@ -0,0 +1,14 @@
+# frozen_string_literal: true
+
+class RemoveCrossOriginUnsafeNoneReferrersSetting < ActiveRecord::Migration[7.1]
+  def up
+    execute <<~SQL
+      DELETE FROM site_settings
+      WHERE name = 'cross_origin_opener_unsafe_none_referrers'
+    SQL
+  end
+
+  def down
+    raise ActiveRecord::IrreversibleMigration
+  end
+end