Add hierarchical discovery with POD concept.

A pod is a group of containers collocated on se same multicast network.
It can be a VM in public cloud or a datacenter in a multi datacenter configuration.
The discovery protocol works by unicast between PODs and multicast inside POD

v0.8.20

bugfix - make msg immutable when using inproc adapter.

Add hierarchical discovery with POD concept.

A pod is a group of containers collocated on se same multicast network.
It can be a VM in public cloud or a datacenter in a multi datacenter configuration.
The discovery protocol works by unicast between PODs and multicast inside POD