Tailscale `Accept DNS` GUI control

[cmcdonald]

I have added a setting to disable accepting DNS configuration from the control server. Tailscale defaults to enabling this option. For most cases where Tailscale is ran on an edge device like pfSense you most likely will want to disable this.

[yobyot]

@cmcdonald

Hi, I wondered if you might add a little more explanation of why it's better to disable Tailscale DNS, especially in the case where subnets are advertised and the pfSense node is an exit node.

Thanks.