fix(x/consensus): Add missing ABCI consensus param in MsgUpdateParams

[facundomedica]

Description

During my audit of baseapp I found that it was not possible to enable vote extensions through a gov proposal. This should address that issue.

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[tac0turtle]

utACK, we should document that this field should be changed only when preparing for enabling VE after a coordinated upgrade. this would happen within the upgrade most likely. @alexanderbez what do you think of limiting this to not be modifiable via these calls

[facundomedica]

utACK, we should document that this field should be changed only when preparing for enabling VE after a coordinated upgrade. this would happen within the upgrade most likely. @alexanderbez what do you think of limiting this to not be modifiable via these calls

I've added the following in UPGRADING.md in another PR: https://github.com/cosmos/cosmos-sdk/pull/16596/files#diff-f411a5009131db5a6c7242b49ca78488f2d274ef9e5e5f4de9262a42108a5386R32-R43

I'll probably add more detail, especially for: - A governance proposal that changes the consensus param.. I'll write there that we need to make sure this happens after an upgrade that adds the functionality

EDIT: updated here: https://github.com/cosmos/cosmos-sdk/blob/7b5cbb71d3b4dc3c8b5aaaf89201ea9085fd14a7/UPGRADING.md#enable-vote-extensions

[alexanderbez]

@tac0turtle yes, I agree. @facundomedica changes make sense to me!

VE will need to be enabled via an explicit software upgrade.