[stable/21.2.x] upgrade/migrations: consensus parameters upgrade handler

[ptrus]

TODO:

• backport go/oasis-test-runner: support for testing update handlers #4179
• bacport [BACPORT/21.2.x] go/roothash: adds ConsensusParameters method #4188

[codecov]

Codecov Report

Merging #4180 (a10f6a3) into stable/21.2.x (3c22b85) will decrease coverage by 0.53%.
The diff coverage is 63.85%.

❗ Current head a10f6a3 differs from pull request most recent head 53e4231. Consider uploading reports for the commit 53e4231 to get more accurate results

@@                Coverage Diff                @@
##           stable/21.2.x    #4180      +/-   ##
=================================================
- Coverage          69.20%   68.67%   -0.54%     
=================================================
  Files                414      415       +1     
  Lines              47428    47511      +83     
=================================================
- Hits               32822    32626     -196     
- Misses             10567    10855     +288     
+ Partials            4039     4030       -9     

Impacted Files	Coverage Δ
go/roothash/api/api.go	84.94% <ø> (ø)
go/staking/api/api.go	62.82% <ø> (ø)
go/upgrade/migrations/consensus_parameters.go	56.86% <56.86%> (ø)
go/consensus/tendermint/roothash/roothash.go	69.57% <60.00%> (-0.11%)	⬇️
go/roothash/api/grpc.go	38.29% <64.70%> (+2.62%)	⬆️
go/consensus/tendermint/apps/roothash/query.go	91.30% <100.00%> (+0.82%)	⬆️
go/roothash/tests/tester.go	90.17% <100.00%> (+0.14%)	⬆️
go/oasis-node/cmd/ias/auth_registry.go	0.00% <0.00%> (-69.24%)	⬇️
...nsensus/tendermint/apps/keymanager/transactions.go	0.00% <0.00%> (-52.95%)	⬇️
go/ias/http/http.go	20.33% <0.00%> (-44.07%)	⬇️
... and 41 more

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