After additional research, it seems like in order to have additional fields added to the DENEB, a new Template is required.

I added the code to the Specification to show a new Column “Importance” but nothing shows as a part of the Ganntt Chart Visual.

{
      "name": "ImportanceColumnWidth",
      "value": 55
    },

Could someone direct me to the right path to create a new Template from DENEB and add the new Column.