Added the description to the credentials generate output

[dgannon991]

What does this change

Optionally displays the description for parameters and credentials in the survey prompt (if present)

The following screengrab was generated with this credential set:

credentials:
 - name: kubeconfig
   path: /home/nonroot/.kube/config
   description: The path to your kubeconfig (usually something like /home/nonroot/.kube/config)
 - name: username
   env: USERNAME

What issue does it fix

Closes #3076

Notes for reviewer

Whilst rebasing the branch I managed to close the original PR somehow (#3112) which is pretty impressively wrong. Apologies. I think I must have pushed up without any commits, and that led to this!

Checklist

• Did you write tests?
• Did you write documentation?
• Did you change porter.yaml or a storage document record? Update the corresponding schema file.
• If this is your first pull request, please add your name to the bottom of our Contributors list. Thank you for making Porter better! 🙇‍♀️

[schristoff]

Tested locally and it worked, would love to see a test that uses the porter.yaml and grabs the description out of that, but it's ndb :)

[dgannon991]

@schristoff - happy to try and get some tests written for that if you'd like (I'm not sure there are any currently due to the interactive nature.) LMK.