Support Setting "Override Local DNS"

[aviau]

I'd like to set "Override Local DNS", which looks like this in the webui:

I would assume a config like this could work:

resource "tailscale_dns_nameservers" "nameservers" {
  override_local_dns = true
  nameservers = [
    "8.8.8.8",
    "1.1.1.1",
  ]
}

[oxtoacart]

@timtailscale has some ideas about this.