Surface which unspecified stage was incorrectly chosen in error message

Proposal

Currently when an user uses a stage name which is not in the specified or default stages it errors with the following message:

Code

When you include a template (or a component now I guess) this message could be more helpful with specifying which stage name was incorrect so you do not have to dig around which stage you probably forgot to add to stages which the template requires:

"#{name} job: chosen stage (#{job[:stage]}) does not exist; available stages are #{@stages.join(", ")}"