Continue committing with a minority of nodes absent

[bagrounds]

My understanding based on the Raft paper is that if cluster size N=3, progress should continue if 1 node is absent.

Gaggle seems to require all 3 nodes to be present to make commits if the cluster size is set to N=3.

Similarly, if the cluster size is set to N=5, 4 nodes seem to be required to make commits, while it should be fine to just have 3.

This can be tested with my demo here