feat!: introduce the consumer-modification handler

[insumity]

Description

Introduces the ConsumerModificationProposal in gaia from ICS (see cosmos/interchain-security#1932 and cosmos/interchain-security#1949).

Testing
After this change we have:

gaiad tx gov submit-legacy-proposal
Error: failed to parse proposal: proposal type is required
Usage:
  gaiad tx gov submit-legacy-proposal [flags]
  gaiad tx gov submit-legacy-proposal [command]

Available Commands:
  cancel-software-upgrade Cancel the current software upgrade proposal
  change-reward-denoms    Submit a change reward denoms proposal
  consumer-addition       Submit a consumer addition proposal
  consumer-modification   Submit a consumer modification proposal
  consumer-removal        Submit a consumer chain removal proposal
  ...

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Author Checklist

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• Included the correct type prefix in the PR title
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• confirmed the correct type prefix in the PR title
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