[Feature] Support auto import modules from registry

[fangyixiao18]

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Motivation

Refer to open-mmlab/mmdetection#9143

Modification

Please briefly describe what modification is made in this PR.

BC-breaking (Optional)

Does the modification introduce changes that break the backward compatibility of the downstream repositories?
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

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects, like MMDet or MMSeg.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Patch coverage: 94.73% and project coverage change: -0.35 ⚠️

Comparison is base (824d62e) 80.61% compared to head (9b0faaa) 80.26%.

❗ Current head 9b0faaa differs from pull request most recent head fcc4dd0. Consider uploading reports for the commit fcc4dd0 to get more accurate results

Additional details and impacted files

@@             Coverage Diff             @@
##           dev-1.x     #660      +/-   ##
===========================================
- Coverage    80.61%   80.26%   -0.35%     
===========================================
  Files          141      141              
  Lines         5127     5129       +2     
  Branches       687      687              
===========================================
- Hits          4133     4117      -16     
- Misses         855      872      +17     
- Partials       139      140       +1     

Flag	Coverage Δ
unittests	80.26% <94.73%> (-0.35%)	⬇️

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

Impacted Files	Coverage Δ
mmselfsup/apis/inference.py	50.00% <50.00%> (ø)
mmselfsup/__init__.py	100.00% <100.00%> (ø)
mmselfsup/registry.py	100.00% <100.00%> (ø)

... and 2 files with indirect coverage changes

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[tonysy]

LGTM