Polish "Add SignalFxConfig source property"

Closes gh-12066

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

@@ -40,7 +40,8 @@ public class SignalFxProperties extends StepRegistryProperties {
 	private String uri;
 
 	/**
-	 * Uniquely identifies the app instance that is publishing metrics to SignalFx. Defaults to the local host name.
+	 * Uniquely identifies the app instance that is publishing metrics to SignalFx.
+	 * Defaults to the local host name.
 	 */
 	private String source;
 
@@ -61,7 +62,7 @@ public class SignalFxProperties extends StepRegistryProperties {
 	}
 
 	public String getSource() {
-		return source;
+		return this.source;
 	}
 
 	public void setSource(String source) {

spring-boot-project/spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -1380,6 +1380,7 @@ content into your application. Rather, pick only the properties that you need.
 	management.metrics.export.signalfx.enabled= # Whether exporting of metrics to this backend is enabled.
 	management.metrics.export.signalfx.num-threads= # Number of threads to use with the metrics publishing scheduler.
 	management.metrics.export.signalfx.read-timeout= # Read timeout for requests to this backend.
+	management.metrics.export.signalfx.source= # Uniquely identifies the app instance that is publishing metrics to SignalFx. Defaults to the local host name.
 	management.metrics.export.signalfx.step=1m # Step size (i.e. reporting frequency) to use.
 	management.metrics.export.signalfx.uri= # Optional custom URI for the SignalFX API.
 	management.metrics.export.simple.mode=cumulative # Counting mode.