go/consensus/tendermint: Add consensus.tendermint.halt_height

[Yawning]

This is equivalent to the cosmos halt-height option, to be used to
bring a node down gracefully at a specific height. Hopefully this will
never need to be used.

[codecov]

Codecov Report

Merging #4793 (aba5861) into master (2a86f51) will decrease coverage by 0.13%.
The diff coverage is 65.21%.

@@            Coverage Diff             @@
##           master    #4793      +/-   ##
==========================================
- Coverage   66.99%   66.85%   -0.14%     
==========================================
  Files         451      451              
  Lines       50289    50300      +11     
==========================================
- Hits        33690    33630      -60     
- Misses      12443    12500      +57     
- Partials     4156     4170      +14     

Impacted Files	Coverage Δ
go/consensus/tendermint/abci/mux.go	58.37% <50.00%> (-1.57%)	⬇️
go/consensus/tendermint/abci/state.go	74.28% <64.70%> (-2.55%)	⬇️
go/consensus/tendermint/full/full.go	66.73% <100.00%> (+1.49%)	⬆️
go/oasis-node/cmd/common/metrics/disk.go	65.51% <0.00%> (-20.69%)	⬇️
go/runtime/host/sandbox/sandbox.go	60.82% <0.00%> (-15.81%)	⬇️
go/oasis-node/cmd/common/metrics/resource.go	84.00% <0.00%> (-8.00%)	⬇️
go/consensus/tendermint/abci/state/state.go	61.53% <0.00%> (-7.70%)	⬇️
go/worker/beacon/tx_retry.go	90.47% <0.00%> (-4.77%)	⬇️
go/common/grpc/grpc.go	79.88% <0.00%> (-4.44%)	⬇️
go/runtime/host/multi/multi.go	70.58% <0.00%> (-4.42%)	⬇️
... and 17 more

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