Integrate with Tailscale Services

[msfjarvis]

Being able to expose caddy-tailscale hosts as Tailscale Services feels like a natural fit and would make the process of managing access a lot easier.

Implemented Tailscale Services in #132

This seems to work well in testing with a fully dynamic configuration:

• 1 node running caddy-tailscale + caddy-docker-proxy
• caddy uses OAuth to create an ephemeral node with a tag tag:caddy
• I created a number of services with tag:service
• auto approval access control: tag:service can automatically accept devices tag:caddy
• containers use labels to bind to a service
• as containers start & stop the service goes up and down automatically