Use parent-based sampler by default

Closes gh-33821

spring-boot-project/spring-boot-actuator-autoconfigure/src/main/java/org/springframework/boot/actuate/autoconfigure/tracing/OpenTelemetryAutoConfiguration.java

@@ -112,7 +112,8 @@ public class OpenTelemetryAutoConfiguration {
 	@Bean
 	@ConditionalOnMissingBean
 	Sampler otelSampler() {
-		return Sampler.traceIdRatioBased(this.tracingProperties.getSampling().getProbability());
+		Sampler rootSampler = Sampler.traceIdRatioBased(this.tracingProperties.getSampling().getProbability());
+		return Sampler.parentBased(rootSampler);
 	}
 
 	@Bean

spring-boot-project/spring-boot-actuator-autoconfigure/src/test/java/org/springframework/boot/actuate/autoconfigure/tracing/OpenTelemetryAutoConfigurationTests.java

@@ -80,6 +80,15 @@ class OpenTelemetryAutoConfigurationTests {
 		});
 	}
 
+	@Test
+	void samplerIsParentBased() {
+		this.contextRunner.run((context) -> {
+			Sampler sampler = context.getBean(Sampler.class);
+			assertThat(sampler).isNotNull();
+			assertThat(sampler.getDescription()).startsWith("ParentBased{");
+		});
+	}
+
 	@ParameterizedTest
 	@ValueSource(strings = { "io.micrometer.tracing.otel", "io.opentelemetry.sdk", "io.opentelemetry.api" })
 	void shouldNotSupplyBeansIfDependencyIsMissing(String packageName) {