[enhancement] show upgrade message

[qrkourier]

It would be helpful for the ziti-tunnel CLI to print a warning message to stderr when an upgrade for the same CPU architecture is available. Here's an example of the message printed by the kOps CLI.

*********************************************************************************

A new kops version is available: 1.21.2
Upgrading is recommended
More information: https://github.com/kubernetes/kops/blob/master/permalinks/upgrade_kops.md#1.21.2

*********************************************************************************

[qrkourier]

@dovholuknf @plorenz I'd be interested in contributing this if you are able to give me some direction and coaching.

[plorenz]

@dovholuknf @plorenz I'd be interested in contributing this if you are able to give me some direction and coaching.

Sure, seems like a nice, user-friendly feature :+1:

[qrkourier]

This was done.