PXD-1906 ⁃ Allow lookup by node category in Peregrine

[philloooo]

Figure out if we can add interfaces (similar to DataNode) for node categories. The fields would be the intersection (or union) of the fields from the nodes in this category

example query:

biospecimen (first: 2) {
  id
  type
} 

result:

{
  "data": {
    "biospecimen": [
      {
         "id": "111",
         "type": "sample"
      },
      {
         "id": "222",
         "type": "read_group"
      }
    ]
  }
}