fix(socketproxy): add Transfer-Encoding: chunked header

In goutils commit 5159888197c5a49605495be9b87525fde26c83d1 Copy with an http.ResponseWriter destination no longer flushes after every write unless Content-Type is text/event-stream, or Transfer-Encoding includes chunked without Content-Length.

This causes endpoints like /events not being flushed on write,
which delays notification like container creation/deletion.

This commit enforces flush on every write for socket proxy,
which also applies to agents

socket-proxy/pkg/handler.go

@@ -34,7 +34,10 @@ func dockerSocketHandler(socket string) http.HandlerFunc {
 		},
 	}
 
-	return rp.ServeHTTP
+	return func(w http.ResponseWriter, r *http.Request) {
+		w.Header().Set("Transfer-Encoding", "chunked")
+		rp.ServeHTTP(w, r)
+	}
 }
 
 func endpointNotAllowed(w http.ResponseWriter, _ *http.Request) {