[types] Add DiscoverySetChangeEvent to deser from ContractEvent
[types] Add DiscoverySetChangeEvent to deser from ContractEvent

Closes: #3354
Approved by: davidiw

aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,libra/libra,aptos-labs/aptos-core,libra/libra,libra/libra,aptos-labs/aptos-core,aptos-labs/aptos-core,aptos-labs/aptos-core