"minecraft:custom" as an item for Datapacks

Instead of adding a whole custom item framework, just add a single item under the ID "minecraft:custom". It would have no way of being obtained outside of commands and wouldn't interact with the world, but would have NBT data that defines things like how long it takes to use and the sound effects from using it. Since scoreboards or advancements can track using items, it just needs to always have a right click event so MCFunction can run commands that make it act like a new item!