DISC protocol enhancements: push sync replication

[Eknir]

The push sync protocol concludes with "replicating" to 3 closest peers. The implementation of this can be improved:

1. The peer that is closest to the chunk pushes to all peers that fall within the PO depth which includes at least 3 peers.
2. Shuffle the concurrency around so that we can check the result of the pusher and ensure that we have at least 3 successful pushes

examples to point 1
PO | peer count
24 | 1
19 | 1
16 | 4
15 | 8
result: push to 6 peers in total (24, 19 and all from 16)

PO | peer count
24 | 1
19 | 1
16 | 1
15 | 8
result: push to 3 peers in total (24, 19 and 16 )

[Eknir]

The research team is currently preparing a proposal for an enhancement of the push sync protocol. That proposal will supersede this one.