[Feature] Support auto import modules from registry.

[sunjiahao1999]

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Motivation

related mmdet PR

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the back-compatibility of the downstream repos?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here, and update the documentation.

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.

[codecov]

Codecov Report

Base: 46.37% // Head: 46.96% // Increases project coverage by +0.59% 🎉

Coverage data is based on head (ef798d4) compared to base (d84e081).
Patch coverage: 67.46% of modified lines in pull request are covered.

❗ Current head ef798d4 differs from pull request most recent head 7e38aa6. Consider uploading reports for the commit 7e38aa6 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           dev-1.x    #2314      +/-   ##
===========================================
+ Coverage    46.37%   46.96%   +0.59%     
===========================================
  Files          259      262       +3     
  Lines        21390    21966     +576     
  Branches      3379     3460      +81     
===========================================
+ Hits          9919    10316     +397     
- Misses       10827    10988     +161     
- Partials       644      662      +18     

Flag	Coverage Δ
unittests	46.96% <67.46%> (+0.59%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

Impacted Files	Coverage Δ
mmdet3d/datasets/transforms/__init__.py	100.00% <ø> (ø)
mmdet3d/evaluation/__init__.py	100.00% <ø> (ø)
mmdet3d/models/dense_heads/fcaf3d_head.py	16.23% <ø> (ø)
mmdet3d/models/detectors/mink_single_stage.py	43.58% <ø> (ø)
mmdet3d/testing/data_utils.py	70.83% <ø> (ø)
mmdet3d/models/voxel_encoders/voxel_encoder.py	38.46% <6.94%> (-12.08%)	⬇️
...t3d/models/data_preprocessors/data_preprocessor.py	39.10% <17.24%> (-5.05%)	⬇️
mmdet3d/datasets/transforms/formating.py	58.03% <33.33%> (+1.78%)	⬆️
mmdet3d/models/data_preprocessors/voxelize.py	33.92% <33.92%> (ø)
mmdet3d/apis/inference.py	14.72% <50.00%> (+0.43%)	⬆️
... and 32 more

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