Feature: Add support for AMQP 0.9.1 "update-secret"

[mortdiggiddy]

Greetings,

I have tested the branch located in amqplib at this github issue:
amqp-node/amqplib#755

The ability to update the secret (password or JWT depending on the application) for the active connection has been verified. I have used an isolated version of the class:

https://github.com/jwalton/node-amqp-connection-manager/blob/master/src/AmqpConnectionManager.ts

To do this. Would you be willing to add a method inside this class that would allow the end user to update the secret? This method would simply forward the call directly to amqplib which can delegate the business logic.