fix(metrics): fix caching agent drift gauge usage (#3747)

Registry.gauge(Id, Number) is deprecated and is for continuously polled
metrics, when what we want is an active gauge that is only published
when available.

clouddriver-aws/src/main/groovy/com/netflix/spinnaker/clouddriver/aws/provider/agent/DriftMetric.java

@@ -16,7 +16,7 @@
 
 package com.netflix.spinnaker.clouddriver.aws.provider.agent;
 
-import com.netflix.spectator.api.Id;
+import com.netflix.spectator.api.Gauge;
 import com.netflix.spectator.api.Registry;
 import com.netflix.spinnaker.clouddriver.aws.security.NetflixAmazonCredentials;
 import org.slf4j.Logger;
@@ -32,9 +32,9 @@ public interface DriftMetric {
 
   String getAgentType();
 
-  default Id getDriftMetricId() {
+  default Gauge getDriftMetricGauge() {
     return getRegistry()
-        .createId(
+        .gauge(
             "cache.drift",
             "agent",
             getClass().getSimpleName(),
@@ -48,7 +48,7 @@ default void recordDrift(Long start) {
     if (start != null && start != 0L) {
       Long drift = getRegistry().clock().wallTime() - start;
       getLog().info("{}/drift - {} milliseconds", getAgentType(), drift);
-      getRegistry().gauge(getDriftMetricId(), drift);
+      getDriftMetricGauge().set(drift);
     }
   }
 }