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>

tailcfg/tailcfg.go

@@ -495,6 +495,7 @@ type Hostinfo struct {
 	Hostname        string         `json:",omitempty"` // name of the host the client runs on
 	ShieldsUp       bool           `json:",omitempty"` // indicates whether the host is blocking incoming connections
 	ShareeNode      bool           `json:",omitempty"` // indicates this node exists in netmap because it's owned by a shared-to user
+	NoLogsNoSupport bool           `json:",omitempty"` // indicates that the user has opted out of sending logs and support
 	GoArch          string         `json:",omitempty"` // the host's GOARCH value (of the running binary)
 	GoVersion       string         `json:",omitempty"` // Go version binary was built with
 	RoutableIPs     []netip.Prefix `json:",omitempty"` // set of IP ranges this client can route

tailcfg/tailcfg_clone.go

@@ -131,6 +131,7 @@ var _HostinfoCloneNeedsRegeneration = Hostinfo(struct {
 	Hostname        string
 	ShieldsUp       bool
 	ShareeNode      bool
+	NoLogsNoSupport bool
 	GoArch          string
 	GoVersion       string
 	RoutableIPs     []netip.Prefix

tailcfg/tailcfg_test.go

@@ -47,6 +47,7 @@ func TestHostinfoEqual(t *testing.T) {
 		"Hostname",
 		"ShieldsUp",
 		"ShareeNode",
+		"NoLogsNoSupport",
 		"GoArch",
 		"GoVersion",
 		"RoutableIPs",

tailcfg/tailcfg_view.go

@@ -266,6 +266,7 @@ func (v HostinfoView) DeviceModel() string    { return v.ж.DeviceModel }
 func (v HostinfoView) Hostname() string       { return v.ж.Hostname }
 func (v HostinfoView) ShieldsUp() bool        { return v.ж.ShieldsUp }
 func (v HostinfoView) ShareeNode() bool       { return v.ж.ShareeNode }
+func (v HostinfoView) NoLogsNoSupport() bool  { return v.ж.NoLogsNoSupport }
 func (v HostinfoView) GoArch() string         { return v.ж.GoArch }
 func (v HostinfoView) GoVersion() string      { return v.ж.GoVersion }
 func (v HostinfoView) RoutableIPs() views.IPPrefixSlice {
@@ -298,6 +299,7 @@ var _HostinfoViewNeedsRegeneration = Hostinfo(struct {
 	Hostname        string
 	ShieldsUp       bool
 	ShareeNode      bool
+	NoLogsNoSupport bool
 	GoArch          string
 	GoVersion       string
 	RoutableIPs     []netip.Prefix