Support for URP? about unity-baked-volumetrics

[frostbone25]

URP support is planned for the near future, but at the moment I'm only focused on core features of the volumetrics toolset which still need work.

The Built-In-Pipeline is indeed old, but it is still used in many applications/games (i.e. VRChat for example), and it's very stable compared to the other pipelines (even newer unity versions still have it). So developing on it means I don't have to worry about API changes and keeping up with them.

With that said though, porting this effect to URP should actually be fairly trivial. There isn't anything overly complex being done on both the toolset or the runtime shaders so it should be pretty easy to do.