Fixes #38410 - Add mechanism for deprecating displayed fields

[qcjames53]

Currently, hammer has no way to deprecate old fields our developers wish to remove. This PR adds an option for deprecating a field with :deprecated => true. When a deprecated field is displayed, a stderr warning message is shown indicating it will be removed in the future. Updated doc/creating_commands.md to show how to deprecate a field.

How to test:

1. Find a field in hammer-cli-foreman or hammer-cli-katello and modify it to have the deprecated flag:

field :example, _("Example field"), Fields::Field, :deprecated => true

2. When displaying this field, verify that a warning is printed to stderr:

WARNING: Field 'Example field' is deprecated and may be removed in future versions.

3. Remove this field from the default set and confirm that the error message does not display when the field is not rendered:

field :example, _("Example field"), Fields::Field, :sets => ['ALL'], :deprecated => true

4. Confirm that the error message does display for a variety of field output edge cases (--fields, etc). Ensure output is always sent to stderr.
5. Add the :replaced_by flag and repeat the previous testing steps:

field :example, _("Example field"), Fields::Field, :replaced_by => "Example/Path"

[ofedoren]

Thanks, @qcjames53 ! This is really a great addition :)

Some nitpicks though:

• Please, use Fixes instead of Refs in this case.
• For deprecated commands and options we also suggest the new command/option to be used instead of deprecated one. Currently the deprecation message for fields is hardcoded with means for removal. Should we also allow a message stating that a deprecated field is being replaced with the new one already, something like we do in
  • https://github.com/theforeman/hammer-cli/blob/master/lib/hammer_cli/options/option_definition.rb#L60
  • https://github.com/theforeman/hammer-cli/blob/master/test/unit/options/option_definition_test.rb#L22-L24
• Could you please add some tests for this feature?

[qcjames53]

@ofedoren Thank you for the review! I have added your requested changes and fixed the commit name.

[ofedoren]

Thanks, @qcjames53 ! We could probably generalize warning message/options instead of hardcoding 2 messages, but that can be dealt with in the future. As of now it seems and works quite nicely.