MinecartMaxSpeed Gamerule converted to an attribute

Change the MinecartMaxSpeed Gamerule to an attribute so multiples minecart can have different speeds
You can also keep the gamerule to set the default speed of a minecart when spawned
This could be useful when fast minecarts breaks older contraptions but you want faster minecarts for travel
(and also a way to change the attribute in survival would be cool but im sure some datapacks will fix that problem)