constructing the expiry Prometheus Item according to new format

Author: Daan Hoogland

plugins/integrations/prometheus/src/main/java/org/apache/cloudstack/metrics/PrometheusExporterImpl.java

@@ -1166,7 +1166,7 @@ class ItemHostCertExpiry extends Item {
         long expiryTimestamp;
 
         public ItemHostCertExpiry(final String zoneName, final String zoneUuid, final String hostName, final String hostUuid, final String hostIp, final long expiry) {
-            super("cloudstack_host_cert_expiry_timestamp");
+            super("cloudstack_host_cert_expiry_timestamp", "Host certificate expiry timestamp in seconds since epoch", "gauge");
             this.zoneName = zoneName;
             this.zoneUuid = zoneUuid;
             this.hostName = hostName;