Make the threashold and shard count configurable.

[v0lkan]

SPIKE Keepers use 3 shards and 2 thresholds as per their shard contribution logic
( for details check out https://zerotohero.dev/spire/spike/shamir-secrets-sharing/ )

It's better to make these configurable through environment variables.

Also it's useful to check out configuration is consistent with the shard number (i.e. if keepers know about 3 peers only but we require 5 shards, it should raise an error).