CLI-specific examples

Provide a way to give CLI-specific examples to an operation. Should use some extension like `x-cli-examples` and you should be able to give a list where the items have both a description and the example itself. These would show up in the help for the command.

Start by locating the operation model and the code that generates command help. Define how an x-cli-examples list carries description and example values, then verify that generated help displays them for the relevant command.

Written by the indexing model from the issue text.