roles/common: Use Abuse.ch's SSL Blacklist in nftables

This adds Abuse.sh's list of IPs using blacklisted SSL certificates
to nftables. These IPs are high confidence indicators of compromise
and we should not route them. The list is updated daily by a systemd
timer.

See: https://sslbl.abuse.ch/blacklist/

roles/common/files/abusech-ipv4.nft

@@ -0,0 +1,5 @@
+#!/usr/sbin/nft -f
+
+define ABUSECH_IPV4 = {
+192.168.254.254
+}