Expose token validation errors when loading folder sets

[slifty]

Right now if I pass a token to /folder that, for whatever reason, can't be properly validated the endpoint acts as though I had not passed a token at all.

The behavior we want is for the endpoint to response with an appropriate error so clients know that something went wrong with authentication.

For example: if FusionAuth returns a 429 error (rate limit), we would want that to translate to a 429 response to the client making a call to stela.