Data-Driven Weather in datapacks

What: exactly what it says in the title, data driven weather types so we can implement weathers that aren't just rain, thunder, or clear

How: add support for a new folder, "weather/" to the "data/" folder of datapacks, with the vanilla datapack including "rain.json" and "thunder.json" in that folder. each json file would then define the characteristics of the weather, whether there's lightning and how frequent it is, the maximum/minimum time the weather can be active/inactive, what texture/movement pattern the weather effects use and whether the effects apply indoors, what sounds it would use, if certain mobs take damage from exposure, whether it lays snow layers, how the sky color is modified, what the sky light level would be, etc. all of which could be defined differently based on biome within the same file. dimension_type definitions would then have a list of what weather shows up in the given dimension.

Why: adding custom weather would be extremely useful for creating custom experiences, you could add stormy rain that looks like it's being blown by wind, fog that uses a half transparent texture to obscure your vision, snow that happens in every biome, acid rain that damages all mobs caught under it, heavier versions of normal weather types that simply use much more dense textures. and don't even get me started with what you could do using these with other datapack features like advancements, functions, and even the data driven enchantments!