Print default values and values list in initial help docs

[Hobart2967]

Is your feature request related to a problem? Please describe.
When running a help command on a values arg or option, no information about possible values is shown. The user has first to fail the command to see the values. I'd like to see them right when asking tusk for help, not when trying to execute and fail.

Also it'll be nice if I could define a usage info for values.

This also concerns the default value, that is never stated.

Describe the solution you'd like

Options:
   -e, --environment <value>  Environment to build the artifact agains. (Default: local) 
                              Valid values: [ stub (USAGE_INFO), local (USAGE_INFO), prod (USAGE_INFO) ]

Additional context

[madhat1]

This will be very useful indeed!