CrowdSec decision list fetched, kept, and its clients banned until the decision ends (closes #106)

SWWAF_CROWDSEC_LAPI_URL and SWWAF_CROWDSEC_LAPI_KEY name an engine whose
decision list, <url>/v1/decisions, is fetched every minute with the key in
X-Api-Key, following no redirect, and kept as a blocklist is: used while a
fetch fails, and across restarts through reputation.json. Ban decisions on an
Ip or a Range end at the fetch time plus their duration. A listed client's
request is refused and bans its netblock with the cause crowdsec until the
decision ends; bans.json, ban notes and metrics take the cause.

Judgement call: fetched every minute, not a setting.
Judgement call: a crowdsec ban never lengthens a limit ban.
Judgement call: a lifted crowdsec ban is remade while its decision lasts.

Model: opus-5-5

internal/state/state.go

@@ -60,7 +60,7 @@ var (
 	errVersion = errors.New("unknown version")
 	// errMissing is for an entry without a field it needs.
 	errMissing     = errors.New("has no")
-	errCause       = errors.New("is not limit, attack or admin")
+	errCause       = errors.New("is not limit, attack, admin or crowdsec")
 	errDestination = errors.New("is not webhook, slack or ntfy")
 	errScope       = errors.New("is not client, net, asn, total or watch")
 	errWaitingList = errors.New(`waiting is a list, but now lists the alerts by ` +
@@ -647,7 +647,7 @@ func (e BanEntry) ban() bans.Ban {
 // worked out, or an expires, which would make it permanent. A permanent
 // ban's expires is null, which Bans cannot tell from a missing one, so
 // each expires is read again as written. A cause other than limit,
-// attack or admin, most likely misspelt, is refused too.
+// attack, admin or crowdsec, most likely misspelt, is refused too.
 func (f *bansFile) check(data []byte) error {
 	var written struct {
 		Bans []struct {
@@ -669,7 +669,8 @@ func (f *bansFile) check(data []byte) error {
 		case written.Bans[i].Expires == nil:
 			return missing(i, "expires")
 		case entry.Cause != "" && entry.Cause != bans.CauseLimit &&
-			entry.Cause != bans.CauseAttack && entry.Cause != bans.CauseAdmin:
+			entry.Cause != bans.CauseAttack && entry.Cause != bans.CauseAdmin &&
+			entry.Cause != bans.CauseCrowdSec:
 			return fmt.Errorf("entry %d's cause %q %w", i+1, entry.Cause, errCause)
 		}
 	}