simulators/eth2: Extract Builder and Clients (#770)

* simulators/eth2/common: extract builder,clients

* simulators/eth2/common: fix validator keys

* simulators/eth2/engine: external library use

* simulators/eth2/withdrawals: external library use

* simulators/eth2: Slot time configuration in common library

* simulators/eth2/engine: remove incremental forks

* simulators/eth2/common: update eth-clients, blockv2 roots

* simulators/eth2/common: fix ttd in testnet, add debug info

* simulators/eth2: Fix spoofing, use newer engine api calls versions

* simulators/eth2/engine: fix getPayloadV2+

* simulators/eth2/common: remove chaingenerator from json marshalling

* simulators/eth2/withdrawals: descriptive errors on getting withdrawals info

* simulators/eth2/common: update mock-builder

Author: marioevz