🧪 Create bevy_volumetrics

[hukasu]

Objective

Continuation of #18637 as part of #18423

Solution

Move code relation to volumetric fog and atmosphere to bevy_volumetrics

Testing

cargo run -p ci
cargo run --example volumetric_fog --features="bevy_volumetrics"
cargo run --example scrolling_fog --features="bevy_volumetrics"
cargo run --example fog_volumes --features="bevy_volumetrics"
cargo run --example atmosphere --features="bevy_volumetrics"

TODO

• Migration Guide

[github-actions]

You added a new feature but didn't update the readme. Please run cargo run -p build-templated-pages -- update features to update it, and commit the file change.