add signet support

[MarnixCroes]

closes #2039

[MarnixCroes]

There is the dedicated Testnet https://docs.wasabiwallet.io/using-wasabi/Testnet.html, chapter. Maybe later this can be expanded into a more general test network document.
Adding a dedicated signet chapter is overkill as it's basically the same as testnet, but for RegTest we could maybe add one.