feat(server): add segment user id (#3193)

Author: jorgeepc

server/analytics/segment.go

@@ -71,9 +71,14 @@ func (t segmentTracker) Track(name string, props map[string]string) error {
 		p = p.Set(k, v)
 	}
 
+	userID := t.serverID
+	if p["user_id"] != nil {
+		userID = p["user_id"].(string)
+	}
+
 	return t.client.Enqueue(segment.Track{
 		Event:      name,
-		UserId:     t.serverID,
+		UserId:     userID,
 		Properties: p,
 		Context: &segment.Context{
 			Direct: true,