swarm: integrate OpenTracing; propagate ctx to internal APIs (#17169)

* swarm: propagate ctx, enable opentracing

* swarm/tracing: log error when tracing is misconfigured

swarm/api/storage.go

@@ -72,7 +72,7 @@ func (s *Storage) Get(ctx context.Context, bzzpath string) (*Response, error) {
 		return nil, err
 	}
 	quitC := make(chan bool)
-	expsize, err := reader.Size(quitC)
+	expsize, err := reader.Size(ctx, quitC)
 	if err != nil {
 		return nil, err
 	}