CLI Testing - Serialize KeyWallet to File

[epiro-ps]

In order to localize CLI testing, we'll need to write the wallet created by plutip to a file for the CLI to read in. This goal of this task is to find or write a function that takes the wallet and writes the JSON file needed to be read by the CLI.

[Geometer1729]

@marijanp was right this needs ctl changes. I made a pr:
Plutonomicon/cardano-transaction-lib#861

[marijanp]

@Geometer1729 I think it is, it should be trivial to serialize the wallet to a .json. But do we also need the CBOR-Hex?

[Geometer1729]

Completed in CTL just use privatePaymentKeyToFile and privateStakeKeyToFile in Contract.Wallet.KeyFile.