Add ECDSA/Eth signing scheme (v1)

[n-hutton]

Pairs with PR: https://github.com/Zilliqa/Zilliqa/pull/2806

The example code examples/evm_transaction_ecdsa.js does the following:

• Moves funds from a genesis address (ZIL) to eth-style
• Makes a payment with this eth style address + ecdsa TX signing
• Executes an EVM transaction using eth signing etc.

[inamirandaz]

@n-hutton why are we merging this to the main branch already?