Rotate tailscale Auth Key

[GrigoriyMikhalkin]

cc @majst01 @Gerrit91

As authentication key has an expiration date we have to rotate it. One approach would be to do it via firewall-controller. It's already connecting to the metal-api and could use the newly introduced v1/vpn/authkey endpoint for rotation.

Problem is, firewall-controller is limited to the Firewall machines. So if we would plan to extend VPN functionality to other machines this setup would have to be reimplemented. My proposal is to implement rotation in metalctl. So that metalctl would be installed on machines, serve as a Tailscale client and would be responsible for authentication key rotation.

Does that sounds good?

[GrigoriyMikhalkin]

cc @majst01 @Gerrit91

That's the only part left to implement. Still up-to discussion.