Helper prompt to add custom configs

[daniel-butler-irl]

There are several widgets that allow a user to display things like a picker in the catalog\projects We should be able to add these with a prompt listing all the available widgets. this example lists available cluster id's

{
              "key": "cluster_id",
              "type": "string",
              "required": true,
              "custom_config": {
                "type": "cluster_var",
                "grouping": "deployment",
                "original_grouping": "deployment"
              }
            }