Comment 2 for bug 918386

Conceptually, could look like this:

options:
    tuning:
        default: 'safe'
        type: enum
        description: 'Tuning level for service'
        selection:
            unsafe: 'Fastest without regards to data'
            fast: 'Balanced saftey/speed’
            safe: 'Data Safe'

Selection defines the enumerated keys, each key is set to a human readable description. This would be rendered in the Juju GUI as a dropdown using the values of each selection key as the value which is displayed to the user.