ADR 016: Validator Consensus Key Rotation

[defihyung]

Description

This PR introduces ADR 016: Validator Consensus Key Rotation, which is the feature for the sake of safer validator key management.

closes: #5233

Related Issues: tendermint/tendermint#1136, #5231

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• Targeted PR against correct branch (see CONTRIBUTING.md)
• Linked to Github issue with discussion and accepted design OR link to spec that describes this work.
• Code follows the module structure standards.
• Wrote unit and integration tests
• Updated relevant documentation (docs/) or specification (x/<module>/spec/)
• Added relevant godoc comments.
• Added a relevant changelog entry to the Unreleased section in CHANGELOG.md
• Re-reviewed Files changed in the Github PR explorer
• Review Codecov Report in the comment section below once CI passes

[robert-zaremba]

AD-16 is missing a status. Is it accepted? According to architecture/README - it's Proposed. So, I suggest firstly to finalize the ADR before doing the review. That being said it's good to have PoC.

cc: @aaronc

[alexanderbez]

I believe it should be accepted, but it can't hurt to be reviewed by newer stewards of the SDK.

#5233

[tac0turtle]

closing this due to staleness. Feel free to reopen when work resumes