UI 2.0: /api/ui/ Endpoint for Model, Filterset Definition to Schema

[bryanculver]

Carved from #2806, Related (and blocking): #3583

Context:

• The model field to filter field mapping at BaseFilterSet.FILTER_DEFAULTS needs to also include the correct UI widget types in the extra for the filter mapping
  • Prototype a JSON representation of the FilterSet to see if we can get away of needing widgets at all for the new UI. JSON Schema would be a good place to start/model from
  • Serve the above representation on the UI API by some convention to the react UI, Ask for a model and get it's filters and their classes and args. We likely will need to advance it to allow for plugin views which define their own filterset (so maybe the view may need to hint that it needs a different filterset than the default one by the model).
  • Build the filterset => widget logic in the React UI, similar to what has been done here:

    nautobot/nautobot/utilities/utils.py

    Line 866 in 0fffa8e

    def get_filterset_parameter_form_field(model, parameter, filterset=None):

    , but in React

This Story:

Addresses that first two points:

• Serializing field definitions into a schema, something like JSONSchema. So:

# For Device's Model Fields
{
   "device_type": {
       "type": "ForeignKey",
       "to": "dcim.DeviceType",
   },
   "name": {
       "type": "CharField"
   }
   "..."
}

• Providing an API endpoint that returns the representation for a provided content type.