Add support for wireguard_include_peers variable

[jelmer]

This allows explicitly setting which peers a node can connect to. If the variable is not present, then all peers are included.

Fixes #195

[jelmer]

That seems reasonable - updated to address your feedback.

[jelmer]

@githubixx any more thoughts on this?

[githubixx]

@jelmer Sorry, I'm currently a little bit short on time. I'll get back to you next week. I need to test the patch first to make sure it has no side effects. But it'd be helpful if you could extend the Molecule test accordingly. You don't have to execute it. It's just for me to have a starting point. Maybe make a copy of the Ubuntu 22.04 host and put it here with adjusted values. And the add the needed variable at the end here. Thanks!