Allow more than one volume replica on a node (as an option)

[jfroy]

Is your feature request related to a problem? Please describe.
On small clusters with a limited number of nodes, or on heterogeneous clusters with storage nodes and compute nodes, it is not possible to replicate a volume on a single node.

Describe the solution you'd like
Add an option to the control-plane to allow more than one volume replica on the same node.

Describe alternatives you've considered

Additional context
Other storage solutions like Ceph and Longhorn support this, though it is not recommended. Cluster operations should have the option to allow nodes to hold more than one replica. Having data storage device redundancy is better than nothing.

[dsharma-dc]

@jfroy I see your point. Yes, that sounds like something which, if the users understand the consequences of, could be provided as an option that has to be explicitly enabled. However, as per the current architecture we'll have to do the feasibility analysis for this.