alphanet: define vAlpha2 consensus parameters

[cce]

Summary

This defines a vAlpha2 consensus protocol, with 3.5s filter timeout and 5MiB block size.

[codecov]

Codecov Report

Merging #4230 (8e710ef) into feature/alphanet (15cdcea) will decrease coverage by 0.04%.
The diff coverage is 100.00%.

@@                 Coverage Diff                  @@
##           feature/alphanet    #4230      +/-   ##
====================================================
- Coverage             54.63%   54.58%   -0.05%     
====================================================
  Files                   391      391              
  Lines                 48790    48796       +6     
====================================================
- Hits                  26654    26635      -19     
- Misses                19910    19936      +26     
+ Partials               2226     2225       -1     

Impacted Files	Coverage Δ
protocol/consensus.go	0.00% <ø> (ø)
config/consensus.go	86.09% <100.00%> (+0.25%)	⬆️
network/wsPeer.go	68.21% <0.00%> (-2.20%)	⬇️
crypto/merkletrie/trie.go	66.42% <0.00%> (-2.19%)	⬇️
agreement/cryptoVerifier.go	67.60% <0.00%> (-2.12%)	⬇️
agreement/proposalManager.go	96.07% <0.00%> (-1.97%)	⬇️
node/node.go	22.38% <0.00%> (-1.94%)	⬇️
crypto/merkletrie/node.go	91.62% <0.00%> (-1.87%)	⬇️
ledger/acctupdates.go	69.43% <0.00%> (+0.65%)	⬆️
data/transactions/verify/txn.go	44.88% <0.00%> (+0.88%)	⬆️

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[egieseke]

Looks good.