Don't replace existing defaultRequestConfigCustomizer

Update `HttpComponentsClientHttpRequestFactoryBuilder` to add to the
existing `defaultRequestConfigCustomizer` rather than replace it.

See gh-43429

spring-boot-project/spring-boot/src/main/java/org/springframework/boot/http/client/HttpComponentsClientHttpRequestFactoryBuilder.java

@@ -182,7 +182,8 @@ public HttpComponentsClientHttpRequestFactoryBuilder withDefaultRequestConfigCus
 			Consumer<RequestConfig.Builder> defaultRequestConfigCustomizer) {
 		Assert.notNull(defaultRequestConfigCustomizer, "'defaultRequestConfigCustomizer' must not be null");
 		return new HttpComponentsClientHttpRequestFactoryBuilder(getCustomizers(), this.httpClientCustomizer,
-				this.connectionManagerCustomizer, this.socketConfigCustomizer, defaultRequestConfigCustomizer,
+				this.connectionManagerCustomizer, this.socketConfigCustomizer,
+				this.defaultRequestConfigCustomizer.andThen(defaultRequestConfigCustomizer),
 				this.tlsSocketStrategyFactory);
 	}
 

spring-boot-project/spring-boot/src/test/java/org/springframework/boot/http/client/HttpComponentsClientHttpRequestFactoryBuilderTests.java

@@ -55,19 +55,25 @@ void withCustomizers() {
 		TestCustomizer<HttpClientBuilder> httpClientCustomizer2 = new TestCustomizer<>();
 		TestCustomizer<PoolingHttpClientConnectionManagerBuilder> connectionManagerCustomizer = new TestCustomizer<>();
 		TestCustomizer<SocketConfig.Builder> socketConfigCustomizer = new TestCustomizer<>();
+		TestCustomizer<SocketConfig.Builder> socketConfigCustomizer1 = new TestCustomizer<>();
 		TestCustomizer<RequestConfig.Builder> defaultRequestConfigCustomizer = new TestCustomizer<>();
+		TestCustomizer<RequestConfig.Builder> defaultRequestConfigCustomizer1 = new TestCustomizer<>();
 		ClientHttpRequestFactoryBuilder.httpComponents()
 			.withHttpClientCustomizer(httpClientCustomizer1)
 			.withHttpClientCustomizer(httpClientCustomizer2)
 			.withConnectionManagerCustomizer(connectionManagerCustomizer)
 			.withSocketConfigCustomizer(socketConfigCustomizer)
+			.withSocketConfigCustomizer(socketConfigCustomizer1)
 			.withDefaultRequestConfigCustomizer(defaultRequestConfigCustomizer)
+			.withDefaultRequestConfigCustomizer(defaultRequestConfigCustomizer1)
 			.build();
 		httpClientCustomizer1.assertCalled();
 		httpClientCustomizer2.assertCalled();
 		connectionManagerCustomizer.assertCalled();
 		socketConfigCustomizer.assertCalled();
+		socketConfigCustomizer1.assertCalled();
 		defaultRequestConfigCustomizer.assertCalled();
+		defaultRequestConfigCustomizer1.assertCalled();
 	}
 
 	@Test