cmd/connector-gen: add helper tool for wide app connector configurations

connector-gen can initially generate connector ACL snippets and
advertise-routes flags for Github and AWS based on their public IP /
domain data.

Updates ENG-2425
Signed-off-by: James Tucker <james@tailscale.com>

cmd/connector-gen/advertise-routes.go

@@ -0,0 +1,22 @@
+// Copyright (c) Tailscale Inc & AUTHORS
+// SPDX-License-Identifier: BSD-3-Clause
+
+package main
+
+import (
+	"fmt"
+	"strings"
+
+	"go4.org/netipx"
+)
+
+func advertiseRoutes(set *netipx.IPSet) {
+	fmt.Println()
+	prefixes := set.Prefixes()
+	pfxs := make([]string, 0, len(prefixes))
+	for _, pfx := range prefixes {
+		pfxs = append(pfxs, pfx.String())
+	}
+	fmt.Printf("--advertise-routes=%s", strings.Join(pfxs, ","))
+	fmt.Println()
+}