Add option for PoS cashu

[Darth-Coin]

Describe the feature

I was testing a bit the Zeus PoS, having 2 LN channels and also a cashu mint added. All the funds received from PoS invoices are going to LN channels. I would like to have an option in the PoS configuration, to select "cashu only" or "LN only". So user can choose and switch between them anytime. If a cashu wallet fail, then can switch to LN channels. Imagine what happen if a mint get busted, then the POS user can switch easily to a LN channel. Or even to a specific mint. For example I want to use a specific mint only for POS...