Feature Request: Have drop down options for ports

[tony-p]

Is your feature request related to a problem? Please describe.
Many input ports often require a valid value from a limited value selection, relying only on free input in these scenarios is fragile and requires intimate knowledge of underlying behaviour

Describe the solution you'd like
It would be great to be able to define options in the imported tree model that could then appear as drop down values in Groot. (Free input should still be allowed to allow for ports instead of constants)

<input_port name="port_name" default="default_value" type="std::string">Port description
  <option>Value_1</option>
  <option>Value_2</option>
  <option>Value_3</option>
</input_port>

This could be used to help solve enum sets (magic enum i already supported on an underlying level), but also string sets. I would also like to use this to inject valid ROS actions/topics/service addresses for node type into the tree model after initial generation to make them available in groot.

Describe alternatives you've considered
This is the only real valid solution I have thought of so far besides sticking with manual free input

Additional context
N/A