Prop 474: Increase stATOM mint cap from 400k USK to 600k USK

This proposal is aimed to increase the stATOM mint cap from 400k USK to 600k USK. stATOM price oracle determination has been proved to be reliable and was battle-tested in different market conditions for the past six months since the launch of this USK market in March 2023.

Discussion: https://discord.com/channels/970650215801569330/1156921021010550794