Better error treatment

[aferreroc]

I am trying to catch errors from the server side, I sent a status "unauthenticated" (code 16) with message "ExpiredSignature"

Received error message from grpc-web-client:
status: Unknown, message: "FetchFailed(JsValue(TypeError: Failed to fetch\nTypeError: Failed to fetch))", details: [], metadata: MetadataMap { headers: {} }

response header:

grpc-status: 16
grpc-message: ExpiredSignature
content-length: 0
date: Mon, 09 Aug 2021 12:06:47 GM

The response header is ok, but the error message needs more treatment, perhaps need to catch response headers and put it into the error message