Fix work groups of depth compute shader

[fredyshox]

What changes do you make in this PR?

The number of work groups in depth_camera.py is fixed to (64, 64, 1), which limits the resolution to (1024, 1024) [=16x64]. The solution is to dynamically calculate the number of work groups based on the image resolution and shader thread group size.

Here's an example showcasing the issue:

sensors = {"depth": (DepthCamera, 1500, 1500)}
env = MetaDriveEnv({
  "image_observation": True,
  "use_render": False,
  "traffic_density": False,
  "stack_size": 1,
  "sensors": sensors,
  "vehicle_config": {
    "image_source": "depth"
  }
})
env.reset()
obs, _, _, _, _ = env.step((0, 0))

plt.imshow(obs["image"][:, :, :, -1])
plt.show()

Checklist

• I have merged the latest main branch into current branch.
• I have run bash scripts/format.sh before merging.
• Please use "squash and merge" mode.

[QuanyiLi]

Great to have this parameter calculated on the fly. Thank you!