[Suggestion] Add some mechanism for appending custom ui game objects when the generic button is clicked

[Yinigma]

One of the stated use cases for the generic button is "use it to open custom menus for your mod," but it provides no access to the game's gui. I don't see another way of injecting a menu into the scene on the button press besides rewriting the hooks already present in this mod, which seems like unnecessary and error-prone duplicated work for anyone with this use case. I'd recommend modifying the current generic button delegate or adding a new menu button class that takes a different type of delegate, and in either case having the delegate return a rect transform or a game object that lethalconfig will then add to the canvas along with some canned means of removing or hiding it once the configuration is finished.