Organize backend into product executable and shared Go modules

backend/product/sessions/model/sessionid.go

@@ -0,0 +1,7 @@
+package model
+
+type SessionIdentifier struct {
+	ClientID       string `bson:"clientId" json:"clientId"`
+	DeviceID       string `bson:"deviceId" json:"deviceId"`
+	SessionVersion string `bson:"sessionVersion,omitempty" json:"sessionVersion,omitempty"`
+}