[c++]: async queue replication feature

[Gordon Sim <gs...@redhat.com>]

I have a requirement for a feature to replicate queue state between 
(clustered) brokers on a primary and DR site that I'm hoping to 
implement over the next couple of weeks.

Attached is some notes through which I've been trying to formulate my 
thoughts. If anyone else has any other thoughts, ideas or comments I'd 
be keen to hear them.

I'm looking for the simplest workable solution, both to minimise the 
amount of time need to implement and to keep things easy to reason about 
to ensure robustness.