Update notice breaks JSON output

[tmfksoft]

Bug description

When automating client management with Headscale using CLI and --output=json the JSON output is 'broken' by the message starting with "An updated version of Headscale has been found" etc, I can't take the JSON output directly.

Is there a flag to disable this output?

While actually updating obviously fixes this I can't sit checking every 5 minutes for an update.

Environment

I'm running Headscale v0.23.0-alpha2 under Ubuntu 22.0.4, though Headscale does need updating.

To Reproduce

Run the command
headscale users list --output=json

[fredrikekre]

headscale users list --output json works (note the missing =) so this is an inconsistency in argument parsing where the real argument parser handles it, but the crude check for machine output here

headscale/cmd/headscale/cli/utils.go

Lines 188 to 196 in 8a8e25a

	func HasMachineOutputFlag() bool {
	for _, arg := range os.Args {
	if arg == "json" || arg == "json-line" || arg == "yaml" {
	return true
	}
	}
	return false
	}

doesn't.