Expand application chart and service configuration values

[richard-cox]

Is your feature request related to a problem? Please describe.
When using dynamically created forms for applications and services the user is presented with something where additional information is required.

For instance...

appListeningPort might be deduced, by there's nothing in google for it (specifically in epinio docs).

Describe the solution you'd like
We would like to improve this by showing placeholder text and a tooltip for the input fields

Describe alternatives you've considered

• add optional description and example fields to AppChart spec.settings entries
• add optional description and example to similar settings for services
• add description and example to the default app chart appListeningPort setting