Lowers the default number of environments for camera envs (#2287)

# Description

Some example environments with rendering required an extensive amount of
VRAM that's likely not available on mid/lower end GPUs. This PR reduces
the default number of environments so that these examples can be more
accessible for users to try. Policy can still train with the lowered
number of environments.

## Type of change

<!-- As you go through the list, delete the ones that are not
applicable. -->

- Bug fix (non-breaking change which fixes an issue)

## Checklist

- [x] I have run the [`pre-commit` checks](https://pre-commit.com/) with
`./isaaclab.sh --format`
- [x] I have made corresponding changes to the documentation
- [x] My changes generate no new warnings
- [ ] I have added tests that prove my fix is effective or that my
feature works
- [ ] I have updated the changelog and the corresponding version in the
extension's `config/extension.toml` file
- [ ] I have added my name to the `CONTRIBUTORS.md` or my name already
exists there

<!--
As you go through the checklist above, you can mark something as done by
putting an x character in it

For example,
- [x] I have done this task
- [ ] I have not done this task
-->

source/isaaclab_tasks/isaaclab_tasks/direct/cartpole/cartpole_camera_env.py

@@ -58,7 +58,7 @@ class CartpoleRGBCameraEnvCfg(DirectRLEnvCfg):
     viewer = ViewerCfg(eye=(20.0, 20.0, 20.0))
 
     # scene
-    scene: InteractiveSceneCfg = InteractiveSceneCfg(num_envs=1024, env_spacing=20.0, replicate_physics=True)
+    scene: InteractiveSceneCfg = InteractiveSceneCfg(num_envs=512, env_spacing=20.0, replicate_physics=True)
 
     # reset
     max_cart_pos = 3.0  # the cart is reset if it exceeds that position [m]

source/isaaclab_tasks/isaaclab_tasks/manager_based/classic/cartpole/cartpole_camera_env_cfg.py

@@ -134,7 +134,7 @@ class TheiaTinyObservationCfg:
 class CartpoleRGBCameraEnvCfg(CartpoleEnvCfg):
     """Configuration for the cartpole environment with RGB camera."""
 
-    scene: CartpoleRGBCameraSceneCfg = CartpoleRGBCameraSceneCfg(num_envs=1024, env_spacing=20)
+    scene: CartpoleRGBCameraSceneCfg = CartpoleRGBCameraSceneCfg(num_envs=512, env_spacing=20)
     observations: RGBObservationsCfg = RGBObservationsCfg()
 
     def __post_init__(self):
@@ -150,7 +150,7 @@ class CartpoleRGBCameraEnvCfg(CartpoleEnvCfg):
 class CartpoleDepthCameraEnvCfg(CartpoleEnvCfg):
     """Configuration for the cartpole environment with depth camera."""
 
-    scene: CartpoleDepthCameraSceneCfg = CartpoleDepthCameraSceneCfg(num_envs=1024, env_spacing=20)
+    scene: CartpoleDepthCameraSceneCfg = CartpoleDepthCameraSceneCfg(num_envs=512, env_spacing=20)
     observations: DepthObservationsCfg = DepthObservationsCfg()
 
     def __post_init__(self):