go/staking/api: Check if thresholds for all kinds are defined in genesis

[tjanez]

Follow up to #2632.

[codecov]

Codecov Report

Merging #2633 into master will decrease coverage by 0.15%.
The diff coverage is 40%.

@@            Coverage Diff            @@
##           master   #2633      +/-   ##
=========================================
- Coverage   63.25%   63.1%   -0.16%     
=========================================
  Files         360     360              
  Lines       34153   34156       +3     
=========================================
- Hits        21604   21554      -50     
- Misses       9895    9924      +29     
- Partials     2654    2678      +24

Impacted Files	Coverage Δ
go/staking/api/sanity_check.go	52.94% <40%> (-0.6%)	⬇️
...consensus/tendermint/apps/roothash/transactions.go	51.68% <0%> (-6.75%)	⬇️
go/control/debug.go	67.74% <0%> (-6.46%)	⬇️
go/consensus/tendermint/apps/staking/query.go	68.57% <0%> (-5.72%)	⬇️
go/common/grpc/auth/auth.go	88.88% <0%> (-5.56%)	⬇️
go/oasis-node/cmd/stake/stake.go	71.05% <0%> (-4.39%)	⬇️
go/runtime/tagindexer/tagindexer.go	68.47% <0%> (-4.35%)	⬇️
go/oasis-node/cmd/debug/storage/storage.go	45.08% <0%> (-3.47%)	⬇️
go/runtime/history/prune.go	74.19% <0%> (-3.23%)	⬇️
go/worker/common/p2p/p2p.go	64.86% <0%> (-2.71%)	⬇️
... and 13 more

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