[FR] - Unify TestnetOptions

[newhoggy]

Internal

Area
cardano-testnet

Describe the feature you'd like
Currently there are multiple versions of TestnetOptions. They differ because the testnets differ in how they be configured.

This feature request seeks to unify them. The act of unifying the options will also involve unifying the testnet code, so considerable thought needs to go into how those very different testnets can be unified.