Binding keys or mouse buttons for hold is not possible anymore. Should be added so we don't need to use autohotkey to fix this. One would assume that this is a no brainer as highly configurable keybinds has been major part of your previous games (you might remember such games as Arma2 and 3).

Allowing bind any action to hold could go along way as you could bind some action to a certain key press to do something and when holding said key you might wanna bind holds breath etc.