[plugin] torch ddp plugin supports sharded model checkpoint

[ver217]

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Closes #3773

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1. torch ddp plugin add save sharded model
2. update related unit test

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[github-actions]

The code coverage for the changed files is 86%.

Click me to view the complete report

Name                                                           Stmts   Miss  Cover
----------------------------------------------------------------------------------
colossalai/booster/plugin/torch_ddp_plugin.py                     63      5    92%
colossalai/checkpoint_io/checkpoint_io_base.py                    66     11    83%
colossalai/checkpoint_io/utils.py                                158     34    78%
tests/test_booster/test_plugin/test_low_level_zero_plugin.py      60      6    90%
tests/test_checkpoint_io/test_torch_ddp_checkpoint_io.py          60      0   100%
----------------------------------------------------------------------------------
TOTAL                                                            407     56    86%