feature: Allow ram clusters, by exposing cluster_node_type

There are some scenarios on which by performance issues is required to have in memory metadata, As RAM nodes don't have to write to disc as much as disc nodes, they can perform better.

As stated on rabbitmq configuration.

However, note that since persistent queue data is always stored on disc, the performance improvements will affect only resource management (e.g. adding/removing queues, exchanges, or vhosts), but not publishing or consuming speed.

We need to expose the cluster_node_type to be defined by the user.