Prop 15: Add Gravity Bridge's native staking token to the Althea EVM

This proposal, if passed, will add the Gravity Bridge staking token Graviton as an allowed token to be moved into the Althea L1 EVM environment. Before voting yes on this proposal check that the contents are correct by querying denom_trace: base_denom: ugraviton path: transfer/channel-0 and ensuring that the resulting denom is ugraviton over the Gravity Bridge channel channel-0.