Rework servers load-balancer to use the WRR

Co-authored-by: Kevin Pollet <pollet.kevin@gmail.com>

pkg/server/service/proxy_test.go

@@ -28,7 +28,7 @@ func BenchmarkProxy(b *testing.B) {
 	req := testhelpers.MustNewRequest(http.MethodGet, "http://foo.bar/", nil)
 
 	pool := newBufferPool()
-	handler, _ := buildProxy(Bool(false), nil, &staticTransport{res}, pool)
+	handler := buildSingleHostProxy(req.URL, false, 0, &staticTransport{res}, pool)
 
 	b.ReportAllocs()
 	for i := 0; i < b.N; i++ {