Add reference layer action

//Add a reference layer:

/**
 *@Param uniqueid [optional] - The unique ID of the incoming reference layer.
 *@Param url [optional] - The URL of the incoming reference layer. If this not set, the portalitemid must be set.
 *@Param portalitemid [optional/required] - The Portal Item ID of the incoming reference layer. This is optional if the url parameter is populated; otherwise it is required.
 *@Param layerid [optional/required] - If the portalitemid is of a feature set, provide the layer ID of the incoming referece layer within that feature set. This is optional if the portalitemid points to a feature layer.
 *@Param referenceLayerID [optional] - Reference an existing layer in your app by its ID to determine which existing layer your incoming layer will be positioned next to. The default position of the incoming layer will be the top of the layer list.
 *@Param newLayerPosition [optional] - Specify if you would like the incoming layer to be positioned "above" or "below" the existing layer.
**/

return {
  command: "add-reference-layer",
  // uniqueid: "",
  url: "//....",
  portalitemid: "...",
  layerid: "",
  referenceLayerID: "",
  newLayerPosition: "below"
};