feat: port-filtering experiment (#891)

Part of https://github.com/ooni/probe/issues/2005

internal/cmd/ooporthelper/ports.go

@@ -0,0 +1,12 @@
+package main
+
+//
+// List of ports we want to use for running integration tests
+//
+
+// Ports for testing the testhelper
+// Note: we must only use unprivileged ports here to ensure tests run successfully
+var TestPorts = []string{
+	"8080", // tcp
+	"5050", // tcp
+}