Store commitments under a prefixed store

[benluelo]

this function:

union/cosmwasm/ibc-union/core/src/contract.rs

Lines 1709 to 1712 in 540e4f6

	fn store_commit(deps: DepsMut, key: &H256, value: &H256) -> Result<(), ContractError> {
	deps.storage.set(key.as_ref(), value.as_ref());
	Ok(())
	}

should use a prefixed store, and not commit directly at the root of the contract. this will allow for more easily iterating the store, and remove any potential collisions with other storages in the contract.

this should probably be implemented as part of the migration to depolama (#3919)