feat: implement multi CA serving

internal/metrics/metrics.go

@@ -26,11 +26,11 @@ var (
 		Buckets: prometheus.ExponentialBuckets(0.0001, 2, 10),
 	}, []string{labelPath})
 
-	CrlEntries = prometheus.NewGauge(prometheus.GaugeOpts{
+	CrlEntries = prometheus.NewGaugeVec(prometheus.GaugeOpts{
 		Namespace: "ocspcrl",
 		Name:      "crl_entries_total",
 		Help:      "Number of entries in the CRL",
-	})
+	}, []string{"ca"})
 )
 
 func init() {