Add missing Stackdriver metric-type-prefix property

Closes gh-36499

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -54,6 +54,12 @@ public class StackdriverProperties extends StepRegistryProperties {
 	 */
 	private boolean useSemanticMetricTypes = false;
 
+	/**
+	 * Prefix for metric type. Valid prefixes are described in the Google Cloud
+	 * documentation (https://cloud.google.com/monitoring/custom-metrics#identifier).
+	 */
+	private String metricTypePrefix = "custom.googleapis.com/";
+
 	public String getProjectId() {
 		return this.projectId;
 	}
@@ -86,4 +92,12 @@ public void setUseSemanticMetricTypes(boolean useSemanticMetricTypes) {
 		this.useSemanticMetricTypes = useSemanticMetricTypes;
 	}
 
+	public String getMetricTypePrefix() {
+		return this.metricTypePrefix;
+	}
+
+	public void setMetricTypePrefix(String metricTypePrefix) {
+		this.metricTypePrefix = metricTypePrefix;
+	}
+
 }

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

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2022 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -60,4 +60,9 @@ public boolean useSemanticMetricTypes() {
 		return get(StackdriverProperties::isUseSemanticMetricTypes, StackdriverConfig.super::useSemanticMetricTypes);
 	}
 
+	@Override
+	public String metricTypePrefix() {
+		return get(StackdriverProperties::getMetricTypePrefix, StackdriverConfig.super::metricTypePrefix);
+	}
+
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/export/stackdriver/StackdriverPropertiesConfigAdapterTests.java

@@ -62,4 +62,12 @@ void whenPropertiesUseSemanticMetricTypesIsSetAdapterUseSemanticMetricTypesRetur
 		assertThat(new StackdriverPropertiesConfigAdapter(properties).useSemanticMetricTypes()).isTrue();
 	}
 
+	@Test
+	void whenPropertiesMetricTypePrefixIsSetAdapterMetricTypePrefixReturnsIt() {
+		StackdriverProperties properties = new StackdriverProperties();
+		properties.setMetricTypePrefix("external.googleapis.com/prometheus");
+		assertThat(new StackdriverPropertiesConfigAdapter(properties).metricTypePrefix())
+			.isEqualTo("external.googleapis.com/prometheus");
+	}
+
 }

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/metrics/export/stackdriver/StackdriverPropertiesTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2012-2021 the original author or authors.
+ * Copyright 2012-2023 the original author or authors.
  *
  * Licensed under the Apache License, Version 2.0 (the "License");
  * you may not use this file except in compliance with the License.
@@ -37,6 +37,7 @@ void defaultValuesAreConsistent() {
 		assertStepRegistryDefaultValues(properties, config);
 		assertThat(properties.getResourceType()).isEqualTo(config.resourceType());
 		assertThat(properties.isUseSemanticMetricTypes()).isEqualTo(config.useSemanticMetricTypes());
+		assertThat(properties.getMetricTypePrefix()).isEqualTo(config.metricTypePrefix());
 	}
 
 }