cli config -- does not show available key options

[njmurarka]

Summary

When I run "cli config", indeed I see I can provide a key and then a value, but I have no idea what keys are available as options. For example, the "keyring-backend" option is a really useful one. Suggestion from @alessio

Problem Definition

It will be helpful to see all the options so I don't have to mine the Internet or the code to see these. It makes usage better.

Proposal

List out the keys and all allowed values and examples in the help for "cli config"

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