Add checkConf&Returns into RoutingCF.addTargetCF

When only `AbstractRoutingConnectionFactory.addTargetConnectionFactory()` is used, 
the `AbstractRoutingConnectionFactory.afterPropertiesSet()` throw an `java.lang.IllegalArgumentException: At least one target factory (or default) is required` 
because the property `confirms` is `null` (the method `addTargetConnectionFactory` doesn't call `checkConfirmsAndReturns` that fill this field).

* add `checkConfirmsAndReturns` into the  `AbstractRoutingConnectionFactory .addTargetConnectionFactory()`
* using `assertThatNoException()` instead of `catch/fail`

**Cherry-pick to `2.4.x` & `2.3.x`**

spring-rabbit/src/main/java/org/springframework/amqp/rabbit/connection/AbstractRoutingConnectionFactory.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2020 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -34,6 +34,7 @@
  * @author Artem Bilan
  * @author Josh Chappelle
  * @author Gary Russell
+ * @author Leonardo Ferreira
  * @since 1.3
  */
 public abstract class AbstractRoutingConnectionFactory implements ConnectionFactory, RoutingConnectionFactory,
@@ -238,6 +239,8 @@ protected void addTargetConnectionFactory(Object key, ConnectionFactory connecti
 		for (ConnectionListener listener : this.connectionListeners) {
 			connectionFactory.addConnectionListener(listener);
 		}
+
+		checkConfirmsAndReturns(connectionFactory);
 	}
 
 	/**

spring-rabbit/src/test/java/org/springframework/amqp/rabbit/connection/RoutingConnectionFactoryTests.java

@@ -1,5 +1,5 @@
 /*
- * Copyright 2002-2019 the original author or authors.
+ * Copyright 2002-2022 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.
@@ -17,6 +17,7 @@
 package org.springframework.amqp.rabbit.connection;
 
 import static org.assertj.core.api.Assertions.assertThat;
+import static org.assertj.core.api.Assertions.assertThatNoException;
 import static org.mockito.ArgumentMatchers.any;
 import static org.mockito.ArgumentMatchers.anyBoolean;
 import static org.mockito.BDDMockito.given;
@@ -51,6 +52,7 @@
  * @author Artem Bilan
  * @author Josh Chappelle
  * @author Gary Russell
+ * @author Leonardo Ferreira
  * @since 1.3
  */
 public class RoutingConnectionFactoryTests {
@@ -323,4 +325,19 @@ protected synchronized void redeclareElementsIfNecessary() {
 		assertThat(SimpleResourceHolder.unbind(connectionFactory)).isEqualTo("foo");
 	}
 
+	@Test
+	void afterPropertiesSetShouldNotThrowAnyExceptionAfterAddTargetConnectionFactory() throws Exception {
+		AbstractRoutingConnectionFactory routingFactory = new AbstractRoutingConnectionFactory() {
+			@Override
+			protected Object determineCurrentLookupKey() {
+				return null;
+			}
+		};
+
+		routingFactory.addTargetConnectionFactory("1", Mockito.mock(ConnectionFactory.class));
+
+		assertThatNoException()
+				.isThrownBy(routingFactory::afterPropertiesSet);
+	}
+
 }