Prop 8: Reduce the unbonding fee to 30 sats/vByte

This governance proposal seeks to reduce the Babylon unbonding transaction fee by introducing a new version of the x/btcstaking module parameters. For full details, please check the corresponding forum post: https://forum.babylon.foundation/t/reduce-babylon-unbonding-fee-rate-from-100-to-30-sats-vbyte/637