Add support for max_stack_size in config (potion)

[Nesseley]

Feature request

Short description Theres an option to make items have custom stack sizes. Add an option so we can give these items trough the config. (Useful for upgrade waves etc.)

Implementation details I currently don't remember the setup of the Config, but I am sure you guys have some great ideas of how to implement this neatly!

Additional info In vanilla you give these items with /give @p minecraft:potion[minecraft:potion_contents=healing,minecraft:max_stack_size=16]