Request tags, with refusing and limits per tag (closes #175)

Each request gets sorted tags from the lookup, new address lists, the
reputation sources and the rule matches, logged as `tags`. New settings:
`SWW_TAG_LISTS`, `SWW_TAG_DENY`, `SWW_TAG_LIMIT_PERCENT`. They replace
`SWW_ASN_LIMIT_PERCENT`, `SWW_COUNTRY_LIMIT_PERCENT` and
`SWW_DENIED_COUNTRIES`. New heuristics `tag_lists` and `tag_deny`; the
latter runs before the rate limits and again after the Core Rule Set.

Model: opus-5-5

internal/discriminator/dnsbl.go

@@ -11,7 +11,8 @@ import (
 )
 
 // dnsbl notes the DNSBL zones whose verdict lists the client, as noteListed
-// does, and refuses the request when SWW_REPUTATION_ACTION is deny. Being
+// does, adds the tag dnsbl=<zone> for each, the zone's key masked, and refuses
+// the request when SWW_REPUTATION_ACTION is deny. Being
 // limit, it lowers the client's limits instead (see limitPercentages), and
 // being log, it does nothing more. A zone without a verdict on the client is
 // asked about it in the background, and the request does not wait for the
@@ -25,6 +26,10 @@ func (dnsbl) check(ctx context.Context, rq *request, _ time.Time) *verdict {
 	rq.dnsblListed = len(listedBy) > 0
 	rq.noteListed(listedBy, "listed by a DNSBL zone")
 
+	for _, zone := range listedBy {
+		rq.addTag("dnsbl=" + zone)
+	}
+
 	if !rq.dnsblListed || rq.h.config.ReputationAction != deny {
 		return nil
 	}