compute servers: support tailscale vpn

[williamstein]

If a user is using tailscale vpn in "the rest of their life", it would be nice if they could easily add a cocalc compute server node to their own tailscale vpn. There's a subtle problems with just doing this on compute servers, since evidently tailscale has its own ssh server (?) that interferes with cocalc's.

RELEVANT: CoCalc does configure and manage a wireguard vpn between all compute servers associated with a project. It would thus be relatively easy to do the above in the "other direction", i.e., instead of using tailscale on cocalc, get users to use wireguard on their own resources to tie them to cocalc.