Include support for apiKey in map.add-layers

Hello,

It would be awesome if the map.add-layers command accepted the Esri apiKey property in the layer(s) definition.

To the best of my knowledge the only options available to add secure content right now are to store an AGOL layer with credentials on your enterprise portal (only works if your organization CORS policy permits it), to add the layer using a workflow which directly queries the REST endpoint, or to provide end users with AGOL credentials to directly access the data (which isn't ideal if your users are already set up using single sign on).

Supplying the apiKey would vastly simplify the process.