Give access to AmqpOutboundEndpoint.RabbitTemplate

Related to spring-cloud/spring-cloud-stream#1824

There are some use-cases when we would like to further customize a
`RabbitTemplate` encapsulated in the `AmqpOutboundEndpoint`.
For this purpose there is just enough to make its getter as `public`.
Also make a `AmqpHeaderMapper` available same way via `public` getter

Author: artembilan

spring-integration-amqp/src/main/java/org/springframework/integration/amqp/outbound/AbstractAmqpOutboundEndpoint.java

@@ -360,7 +360,7 @@ protected ExpressionEvaluatingMessageProcessor<String> getExchangeNameGenerator(
 		return this.exchangeNameGenerator;
 	}
 
-	protected AmqpHeaderMapper getHeaderMapper() {
+	public AmqpHeaderMapper getHeaderMapper() {
 		return this.headerMapper;
 	}
 

spring-integration-amqp/src/main/java/org/springframework/integration/amqp/outbound/AmqpOutboundEndpoint.java

@@ -98,7 +98,7 @@ public String getComponentType() {
 
 
 	@Override
-	protected RabbitTemplate getRabbitTemplate() {
+	public RabbitTemplate getRabbitTemplate() {
 		return this.rabbitTemplate;
 	}