support all types of animation interpolation from gltf (#10755)

# Objective

- Support step and cubic spline interpolation from gltf

## Solution

- Support step and cubic spline interpolation from gltf

Tested with
https://github.com/KhronosGroup/glTF-Sample-Models/tree/master/2.0/InterpolationTest
expected: 

![](https://raw.githubusercontent.com/KhronosGroup/glTF-Sample-Models/master/2.0/InterpolationTest/screenshot/screenshot.gif)
result: 

![output](https://github.com/bevyengine/bevy/assets/8672791/e7f1afd5-20c9-4921-97d4-8d0c82203068)

---

## Migration Guide

When manually specifying an animation `VariableCurve`, the interpolation
type must be specified:

- Bevy 0.12
```rust
        VariableCurve {
            keyframe_timestamps: vec![0.0, 1.0, 2.0, 3.0, 4.0],
            keyframes: Keyframes::Rotation(vec![
                Quat::IDENTITY,
                Quat::from_axis_angle(Vec3::Y, PI / 2.),
                Quat::from_axis_angle(Vec3::Y, PI / 2. * 2.),
                Quat::from_axis_angle(Vec3::Y, PI / 2. * 3.),
                Quat::IDENTITY,
            ]),
        },
```

- Bevy 0.13
```rust
        VariableCurve {
            keyframe_timestamps: vec![0.0, 1.0, 2.0, 3.0, 4.0],
            keyframes: Keyframes::Rotation(vec![
                Quat::IDENTITY,
                Quat::from_axis_angle(Vec3::Y, PI / 2.),
                Quat::from_axis_angle(Vec3::Y, PI / 2. * 2.),
                Quat::from_axis_angle(Vec3::Y, PI / 2. * 3.),
                Quat::IDENTITY,
            ]),
            interpolation: Interpolation::Linear,
        },
```

src/loader.rs

@@ -205,20 +205,18 @@ async fn load_gltf<'a, 'b, 'c>(
 
     #[cfg(feature = "bevy_animation")]
     let (animations, named_animations, animation_roots) = {
-        use bevy_animation::Keyframes;
+        use bevy_animation::{Interpolation, Keyframes};
         use gltf::animation::util::ReadOutputs;
         let mut animations = vec![];
         let mut named_animations = HashMap::default();
         let mut animation_roots = HashSet::default();
         for animation in gltf.animations() {
             let mut animation_clip = bevy_animation::AnimationClip::default();
             for channel in animation.channels() {
-                match channel.sampler().interpolation() {
-                    gltf::animation::Interpolation::Linear => (),
-                    other => warn!(
-                        "Animation interpolation {:?} is not supported, will use linear",
-                        other
-                    ),
+                let interpolation = match channel.sampler().interpolation() {
+                    gltf::animation::Interpolation::Linear => Interpolation::Linear,
+                    gltf::animation::Interpolation::Step => Interpolation::Step,
+                    gltf::animation::Interpolation::CubicSpline => Interpolation::CubicSpline,
                 };
                 let node = channel.target().node();
                 let reader = channel.reader(|buffer| Some(&buffer_data[buffer.index()]));
@@ -264,6 +262,7 @@ async fn load_gltf<'a, 'b, 'c>(
                         bevy_animation::VariableCurve {
                             keyframe_timestamps,
                             keyframes,
+                            interpolation,
                         },
                     );
                 } else {