Fix links to Spring AMQP's javadoc

[jourteen]

Following links from AMQP section of Spring Boot Reference lead to 404 error page:

• https://docs.spring.io/spring-amqp/docs/3.1.5/api/rabbit/core/RabbitMessagingTemplate.html
• https://docs.spring.io/spring-amqp/docs/3.1.5/api/rabbit/annotation/EnableRabbit.html

The correct links are:

• https://docs.spring.io/spring-amqp/docs/3.1.5/api/org/springframework/amqp/rabbit/core/RabbitMessagingTemplate.html
• https://docs.spring.io/spring-amqp/docs/3.1.5/api/org/springframework/amqp/rabbit/annotation/EnableRabbit.html

[wilkinsona]

Thanks for noticing and reporting this, @jourteen.