Add RabbitMQ Connection Timeout Property

Fixes gh-685
Closes gh-5791

spring-boot-docs/src/main/asciidoc/appendix-application-properties.adoc

@@ -841,6 +841,7 @@ content into your application; rather pick only the properties that you need.
 	spring.rabbitmq.cache.channel.size= # Number of channels to retain in the cache.
 	spring.rabbitmq.cache.connection.mode=CHANNEL # Connection factory cache mode.
 	spring.rabbitmq.cache.connection.size= # Number of connections to cache.
+	spring.rabbitmq.connection-timeout= # Connection Timeout, in milliseconds.
 	spring.rabbitmq.dynamic=true # Create an AmqpAdmin bean.
 	spring.rabbitmq.host=localhost # RabbitMQ host.
 	spring.rabbitmq.listener.acknowledge-mode= # Acknowledge mode of container.