Add ability to terminate TLS with tailscale cert.

[colek42]

The load balancer should configure HA proxy with certificates obtained from tailscale cert {hostname}

[colek42]

I got this working as a POC with caddy here: https://github.com/testifysec/tailscale-svc-lb. I need to clean it up a bit, and store the certs as secrets.

I'll make a PR when it is ready.

[clrxbl]

Personally not a user of Tailscale TLS certificates but I can see the appeal of this + Caddy/HAProxy.
Initially this project used HAProxy but I switched over to iptables DNAT since I managed to make it work for my usecase.

Feel free to PR something once it's ready.

[cedi]

I am doing this by having cert-manager configured with a DNS01 challenge to obtain a letsencrypt certificate