tstest/natlab/vnet: add start of virtual network-based NAT Lab

Updates #13038

Change-Id: I3c74120d73149c1329288621f6474bbbcaa7e1a6
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

gokrazy/tsapp/config.json

@@ -1,16 +1,21 @@
 {
     "Hostname": "tsapp",
-    "Update": { "NoPassword": true },
+    "Update": {
+        "NoPassword": true
+    },
     "SerialConsole": "ttyS0,115200",
     "Packages": [
         "github.com/gokrazy/serial-busybox",
         "github.com/gokrazy/breakglass",
         "tailscale.com/cmd/tailscale",
-        "tailscale.com/cmd/tailscaled"
+        "tailscale.com/cmd/tailscaled",
+        "tailscale.com/cmd/tta"
     ],
     "PackageConfig": {
         "github.com/gokrazy/breakglass": {
-            "CommandLineFlags": [ "-authorized_keys=ec2" ]
+            "CommandLineFlags": [
+                "-authorized_keys=ec2"
+            ]
         },
         "tailscale.com/cmd/tailscale": {
             "ExtraFilePaths": {
@@ -21,4 +26,4 @@
     "KernelPackage": "github.com/tailscale/gokrazy-kernel",
     "FirmwarePackage": "github.com/tailscale/gokrazy-kernel",
     "InternalCompatibilityFlags": {}
-}
+}