Extreme EX-OS support

[gerivives]

Dear Community,

They say you loose nothing for asking, so... I believe it would be a great idea to have Extreme EX-OS support in Containerlab natively. I would go on to do it myself but I am not an expert in this topic, thus I am just suggesting it.

If anyone else may be interested, let others know by posting here :).

Thanks!

[rafabr]

I've opened a PR to add support for EXOS (#271). Give it a try and let me know if it works for you!