Currently, hammer has no way to deprecate old fields our developers wish to remove. Add an option for deprecating a field. When a deprecated field is displayed, add a stderr warning message indicating it will be removed in the future. Update `doc/creating_commands.md` to show how to deprecate a field.

Redmines:

https://projects.theforeman.org/issues/38410

https://projects.theforeman.org/issues/38427

GitHub PRs:

https://github.com/theforeman/hammer-cli/pull/395

https://github.com/theforeman/hammer-cli/pull/397