Make AA Amphib boats have a float function where they cannot move - but can fire

[mild pendant]

Zero-K gadget which would enable this functionality

https://github.com/ZeroK-RTS/Zero-K/blob/master/LuaRules/Gadgets/unit_float_toggle.lua

[lost marlin]

i believe we are against toggles that constraint movement, so no artillery that can only fire when stationary and same for this