Add option to include portlet preferences in API endpoints

[bjagg]

Is your feature request related to a problem? Please describe.
Some deployers would like to access portlet preferences in their front-end code.

Describe the solution you'd like
Add an optional flag that will turn on portlet preferences in the same API endpoints that deliver portlet parameters.

Describe alternatives you've considered
A clear and concise description of any alternative solutions or features you've considered.

Additional context
This was originally avoided due to some deployers saving passwords and other sensitive information in these fields. It is important to disable this by default.