Worldgen should allow custom base materials for portals.

Since it's now possible to create custom dimensions as of 20w21a, I would like to suggest allowing the worldgen json to say "a nether portal made out of this material, e.g. crying obsidian, would be able to be used to travel between this custom dimension and another dimension".

An example of what I'm trying to do with commands right now is, I'm trying to make a nether portal frame with crying obsidian and when it is lit with nether portal blocks, it would allow me to travel to my custom dimension.

I can currently detect when a player steps on crying obsidian and if there's a nether portal block above it, but I'm not able to detect when a player uses flint and steel on the crying obsidian. My goal is to make the portal work exactly as the vanilla obsidian portal, but it would take me to my own custom dimension instead.

I would also like to suggest being able to choose the coordinate manipulation like how the nether portal has a 1:8 ratio. This ratio would be chosen by the world gen json.