feat: tlsmiddlebox experiment (#817)

See https://github.com/ooni/probe/issues/2124

internal/engine/experiment/tlsmiddlebox/utils.go

@@ -0,0 +1,25 @@
+package tlsmiddlebox
+
+//
+// Utility functions for tlsmiddlebox
+//
+
+import (
+	"net"
+)
+
+// prepareAddrs prepares the resolved IP addresses by
+// adding the configured port as a prefix
+func prepareAddrs(addrs []string, port string) (out []string) {
+	if port == "" {
+		port = "443"
+	}
+	for _, addr := range addrs {
+		if net.ParseIP(addr) == nil {
+			continue
+		}
+		addr = net.JoinHostPort(addr, port)
+		out = append(out, addr)
+	}
+	return
+}