feat!: add initial deposit ratio requirement of 0.5 for proposal submission

[crypin]

Description

The MinInitialDepositRatio is set to 0.5, which verifies that the initial deposition is more than 50% of the params.MinDeposit when submitting the proposal.

MinInitialDepositRatio was added as a parameter in cosmos#12771
We also need the function, but it has not been released yet, so we added it by hardcoding it to 0.5 instead of param.
The reason why it is not added to the parameter is to minimize store migration to reduce upgrade complexity and preserve the original params structure.

Ref

• feat!: initial deposit requirement for proposals cosmos/cosmos-sdk#12771

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[richard-bachman]

Thank you for drafting. Please see my comments.