cmd/tailscaled, tailcfg, hostinfo: add flag to disable logging + support

As noted in #5617, our documented method of blocking log.tailscale.io
DNS no longer works due to bootstrap DNS.

Instead, provide an explicit flag (--no-logs-no-support) and/or env
variable (TS_NO_LOGS_NO_SUPPORT=true) to explicitly disable logcatcher
uploads. It also sets a bit on Hostinfo to say that the node is in that
mode so we can end any support tickets from such nodes more quickly.

This does not yet provide an easy mechanism for users on some
platforms (such as Windows, macOS, Synology) to set flags/env. On
Linux you'd used /etc/default/tailscaled typically. Making it easier
to set flags for other platforms is tracked in #5114.

Fixes #5617
Fixes tailscale/corp#1475

Change-Id: I72404e1789f9e56ec47f9b7021b44c025f7a373a
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>

cmd/tailscaled/tailscaled.go

@@ -113,6 +113,7 @@ var args struct {
 	verbose        int
 	socksAddr      string // listen address for SOCKS5 server
 	httpProxyAddr  string // listen address for HTTP proxy server
+	disableLogs    bool
 }
 
 var (
@@ -144,6 +145,7 @@ func main() {
 	flag.StringVar(&args.socketpath, "socket", paths.DefaultTailscaledSocket(), "path of the service unix socket")
 	flag.StringVar(&args.birdSocketPath, "bird-socket", "", "path of the bird unix socket")
 	flag.BoolVar(&printVersion, "version", false, "print version information and exit")
+	flag.BoolVar(&args.disableLogs, "no-logs-no-support", false, "disable log uploads; this also disables any technical support")
 
 	if len(os.Args) > 0 && filepath.Base(os.Args[0]) == "tailscale" && beCLI != nil {
 		beCLI()
@@ -199,6 +201,10 @@ func main() {
 		args.statepath = paths.DefaultTailscaledStateFile()
 	}
 
+	if args.disableLogs {
+		envknob.SetNoLogsNoSupport()
+	}
+
 	if beWindowsSubprocess() {
 		return
 	}