In 1.13, Mojang added datapacks to the base game. They allow for the modification of the files placed under resources/data. This includes advancements, loot tables, structures, recipes, tags, and more in the future. Forge, and your mod, are also datapacks. Any user can therefore modify all the recipes, loot tables, and other data of a mod just like with resource packs.
Therefore, there is little sense in having configurable recipes or mob drops. Any user can modify them to any value (even from other mods).
In your project, you have a folder “resources” that has to contain a folder “data”. This folder will be your datapack. Your mod can have multiple data domains, since you can add or modify already existing datapacks, like vanilla’s, Forge’s, or another mod’s.
Additional reading on resources can be found here.
To modify a datapack (be it the end-user or in dev), you need to know the mod ID and the registry name of the item/mob/advancement that you want to override. These can be found after launching the mod (F3+H), but providing it for users in a simpler way can be helpful (using GitHub will allow users to navigate the datapack you provide with the mod). You can then follow the steps found here to create any datapack.