| Protocol to discover subgroups; e.g., existing due to a network partition (that healed). Example: group
{p,q,r,s,t,u,v,w} is split into 3 subgroups {p,q}, {r,s,t,u} and {v,w}. This protocol will eventually send
a MERGE event with the coordinators of each subgroup up the stack: {p,r,v}. Note that - depending on the time
of subgroup discovery - there could also be 2 MERGE events, which first join 2 of the subgroups, and then the
resulting group to the last subgroup. The real work of merging the subgroups into one larger group is done
somewhere above this protocol (typically in the GMS protocol).
This protocol works as follows:
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