rails: update framework files and settings to 7.0.

* Update framework files with `bin/rails app:update`.
* Update to use new Rails 7.0 default settings, except for a couple
  things regarding new cookie and cache formats that would prevent us
  from rolling back to Rails 6.1 if necessary.

bin/rails

@@ -1,4 +1,4 @@
 #!/usr/bin/env ruby
-APP_PATH = File.expand_path('../config/application', __dir__)
+APP_PATH = File.expand_path("../config/application", __dir__)
 require_relative "../config/boot"
 require "rails/commands"