Allow AdvertiseTags to be passed to tsnet.Server

[chrishoage]

Closes #48

This PR Bumps the tsnet go module to v1.90.6 to include tailscale/tailscale@b9cda4b

This update allows tsnet to accept oauth client secrets to be passed in place of the auth key.

This also takes advantage of tailscale/tailscale#8531 to allow setting arbitrary advertise tags.

Both of these allow for a minimal change set to close the PR

I suppose this MR would supersede #109

I did this for my own caddy-tailscale use, but figured opening the PR may be worth while. I applied the feedback in the linked PR along with adding some tests

{
	log tailscale {
    level DEBUG
  }
  tailscale {
    ephemeral
		tags tag:test tag:container

		test-caddy {
			port 41650
		}
		other-caddy {
			port 41651
			tags tag:test tag:test-sub
		}
		more-other-caddy {
			port 41652
		}
  }
}

:80 {
  bind tailscale/test-caddy
  respond OK
}
:80 {
  bind tailscale/other-caddy
  respond OK
}

:80 {
  bind tailscale/more-other-caddy
  respond OK
}

I have validated these changes function as expected

[willnorris]

man, this looks great! Thanks!