Create a setting for heartbeat

[man0l]

Heartbeats helps the server to identify the inactive connections: https://www.rabbitmq.com/heartbeats.html

The default amqp library has itself default setting for heartbeat: https://github.com/ricbra/rabbitmq-cli-consumer/blob/master/consumer/consumer.go#L219

But it would be great to be setting in the configuration file.