Add reference layer action

//Add a reference layer
return {
    command: "add-reference-layer",
    // "uniqueid": "<theid>", // can be used to remove
    url: "//....", // if not set mustuse portalitemid and layerid (if fs layer),
    portalitemid: "...", // optional if url is use
    layerid: "2" // if fs service. Need the particular layer
};