[ASB] proposal to change how state flows through the broker

What

During work on the last_operation description, I realised there was an issue with the current way data flows through the system from the Job to etcd
See https://github.com/openshift/ansible-service-broker/issues/638
for (alot) more context.
On the back of that I proposed a change to the design of the broker that I then discussed with the broker team. In order to get change done and communicated well, it is best to create a proposal outlining the needed changes.