Turn staking Power Reduction into an on-chain param

[sunnya97]

Summary

Background: #7655

Currently, the power reduction variable in the staking module is defaulted to 10^6. While it is possible to change this in the app.go in the codebase, we would like to remove the reliance on global variables throughout the codebase. Instead, the power reduction should be an on-chain param.

Along with better code hygiene, by making PowerReduction an on-chain param instead of code variable, we would be able to update it on a running chain. This could be useful for things like asset redenominations, but also more advanced voting power distributions.

For example, you can use a dynamic PowerReduction to create a "less granular" voting power (i.e. if Validator A has a stake 54 tokens, and validator B has stake 103 tokens, the chain can dynamically set the power reduction to be 50, so validator A has voting power 1, and validator B has voting power 2.). This is useful for things like threshold cryptography and sharding.

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[amaury1093]

This change causes a consensus failure: #9447. The current decision is that we'll revert if for now, i.e. won't include it in v0.43.

Re-opening as to find a strategy to include this feature in v0.44.