Allow adding arbitrary arguments in advanced mode

[mijofa]

I like the RetroArch Forwarder mode, but was hoping to do similar for Moonlight-Switch, which has support for a similar style of argument handling per: https://github.com/XITRIX/Moonlight-Switch?tab=readme-ov-file#nsp-forwarder

Would likely become impractical if you started trying to add support for all such types of apps, but just allowing arbitrary arguments to be added would allow people to sort it out themselves.