feat: add -auto-transmit flag to start transmitting on connect

When -auto-transmit is passed, barnard automatically keys up the
microphone as soon as the connection sync completes. Useful for
testing, bots, and unattended operation.

Usage:
  barnard -auto-transmit -server=mumble.example.com -username=test_bot

main.go

@@ -116,6 +116,7 @@ func main() {
 	buffers := flag.Int("buffers", 16, "number of audio buffers to use")
 	profile := flag.Bool("profile", false, "add http server to serve profiles")
 	noiseSuppressionEnabled := flag.Bool("noise-suppression", false, "enable noise suppression for microphone input")
+	autoTransmit := flag.Bool("auto-transmit", false, "start transmitting immediately on connect")
 	logLevel := flag.String("log", "warn", "log level: debug, info, warn, error")
 	logFile := flag.String("logfile", "", "write logs to this file (in addition to stderr)")
 
@@ -208,6 +209,7 @@ func main() {
 		Config:          gumble.NewConfig(),
 		UserConfig:      userConfig,
 		Address:         *server,
+		AutoTransmit:    *autoTransmit,
 		MutedChannels:   make(map[uint32]bool),
 		NoiseSuppressor: noise.NewSuppressor(),
 	}