support upgrade to tendermint 0.35

[yaruwangway]

Summary

support key migration when upgrade to tendermint 0.35

Problem Definition

In Tendermint 0.35, the format of keys in the database are changed. Operators who are running nodes that started as 0.34 will need to migrate the key formats.

Proposal

Gaia will migrate the key format through pre-upgrade handler in cosmovisor before execute the new binary. We could use cosmovisor with a flag --pre-upgrade-hook to run a script to migrate the key.

TODO:

• add key migration cli
• define the pre-upgrade handler and the script to run for migration
• tests

Ref:
cosmos/cosmos-sdk#10047

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[mmulji-ic]

v0.35 developed put on hold, in favour of v0.36.