chore: Extend the ProtoMsg.Error schema with a status field

The status hint code is a necessary hint for the server to determine
what status to return.

Signed-off-by: Alf-Rune Siqveland <alf.rune@northern.tech>

ws/protomsg.go

@@ -102,6 +102,8 @@ type Error struct {
 	Error string `msgpack:"err" json:"error"`
 	// Close determines whether the session closed as a result of this error.
 	Close bool `msgpack:"close" json:"close"`
+	// Status is an upstream status hint of the equivalent HTTP status code.
+	Status int `msgpack:"status,omitempty" json:"status,omitempty"`
 	// MessageProto is the protocol of the message that caused the error.
 	MessageProto ProtoType `msgpack:"msgproto,omitempty" json:"message_protocol,omitempty"`
 	// Type of message that raised the error