Add publishUnchangedMeters StatsD support

Add configuration property to support publishing unchanged pollable
meters.

See gh-11967

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/statsd/StatsdProperties.java

@@ -59,7 +59,8 @@ public class StatsdProperties {
 
 	/**
 	 * How often gauges will be polled. When a gauge is polled, its value is recalculated
-	 * and if the value has changed, it is sent to the StatsD server.
+	 * and if the value has changed (or publishUnchangedMeters is true),
+	 * it is sent to the StatsD server.
 	 */
 	private Duration pollingFrequency = Duration.ofSeconds(10);
 
@@ -68,6 +69,11 @@ public class StatsdProperties {
 	 */
 	private Integer queueSize = Integer.MAX_VALUE;
 
+	/**
+	 * Send unchanged meters to the StatsD server.
+	 */
+	private Boolean publishUnchangedMeters = true;
+
 	public Boolean getEnabled() {
 		return this.enabled;
 	}
@@ -124,4 +130,11 @@ public class StatsdProperties {
 		this.queueSize = queueSize;
 	}
 
+	public Boolean getPublishUnchangedMeters() {
+		return this.publishUnchangedMeters;
+	}
+
+	public void setPublishUnchangedMeters(Boolean publishUnchangedMeters) {
+		this.publishUnchangedMeters = publishUnchangedMeters;
+	}
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/metrics/export/statsd/StatsdPropertiesConfigAdapter.java

@@ -78,4 +78,8 @@ public class StatsdPropertiesConfigAdapter
 		return get(StatsdProperties::getQueueSize, StatsdConfig.super::queueSize);
 	}
 
+	@Override
+	public boolean publishUnchangedMeters() {
+		return get(StatsdProperties::getPublishUnchangedMeters, StatsdConfig.super::publishUnchangedMeters);
+	}
 }