outbound firewall rule UI for SPR's output chain

[lts-rad]

we recently added conntrack abuse hardening to the OUTPUT chain.

  chain OUTPUT {
    type filter hook output priority 0; policy accept
    oifname @uplink_interfaces ip daddr @supernetworks goto DROPLOGOUTP
    oifname @uplink_interfaces ip saddr @supernetworks goto DROPLOGOUTP
  }

let's further expand on this and let users populate output rules from the SPR UI/ API.