Deprecation support for file and yaml configurations

We don't have yet support for deprecate the use of port files nor to decomission specific configuration attributes on the gdk.yml.

Proposal

Add deprecation_message support when reading port files so we can remove them in the future, as well as a similar solution for gdk.yml configurations.

Here is an example usage/draft of the DSL usage:

class Config < ConfigSettings

  # deprecating a port file
  port { read!('some_port_file', deprecation_message: 'Set port in gdk.yml') }

  # deprecating a renamed variable
  group do
    old { nil }
    new { deprecated_config!('group', 'old', deprecation_message: "Use 'group.new' instead") || 'some default value' }
  end
end