[Fix] Fix ImVoxelNet and KittiMetric & refactor configs of ImVoxelNet

[JingweiZhang12]

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Motivation

Fix some bugs in ImVoxelNet and KittiMetric, simplify the configs of ImVoxelNet and replace all convert_to_datasample with add_pred_to_datasample for keeping consistency with mmdet

Modification

BC-breaking (Optional)

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Checklist

1. Pre-commit or other linting tools are used to fix the potential lint issues.
2. The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
3. If the modification has potential influence on downstream projects, this PR should be tested with downstream projects.
4. The documentation has been modified accordingly, like docstring or example tutorials.