config validation command

It would be valuable to add a command in the CLI that validates the supplied config. It can also return an example of the commands that could be run (as we use `template` and let the user pass in variables that we fill prior to running).

Start by locating the CLI command entry points and the existing config and template-variable handling. Define validation behavior and the example commands that should be returned, then verify the command accepts supplied configuration and reports actionable results.

Written by the indexing model from the issue text.