ipn: add user pref for running web client

This is not currently exposed as a user-settable preference through
`tailscale up` or `tailscale set`.  Instead, the preference is set when
turning the web client on and off via localapi. In a subsequent commit,
the pref will be used to automatically start the web client on startup
when appropriate.

Updates tailscale/corp#14335

Signed-off-by: Will Norris <will@tailscale.com>

ipn/conf.go

@@ -36,6 +36,7 @@ type ConfigVAlpha struct {
 
 	PostureChecking opt.Bool         `json:",omitempty"`
 	RunSSHServer    opt.Bool         `json:",omitempty"` // Tailscale SSH
+	RunWebClient    opt.Bool         `json:",omitempty"`
 	ShieldsUp       opt.Bool         `json:",omitempty"`
 	AutoUpdate      *AutoUpdatePrefs `json:",omitempty"`
 	ServeConfigTemp *ServeConfig     `json:",omitempty"` // TODO(bradfitz,maisem): make separate stable type for this
@@ -113,6 +114,10 @@ func (c *ConfigVAlpha) ToPrefs() (MaskedPrefs, error) {
 		mp.RunSSH = c.RunSSHServer.EqualBool(true)
 		mp.RunSSHSet = true
 	}
+	if c.RunWebClient != "" {
+		mp.RunWebClient = c.RunWebClient.EqualBool(true)
+		mp.RunWebClientSet = true
+	}
 	if c.ShieldsUp != "" {
 		mp.ShieldsUp = c.ShieldsUp.EqualBool(true)
 		mp.ShieldsUpSet = true