[Refactor] Change resources directory to .mim

[zhouzaida]

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Motivation

Change the resources directory to package/.mim rather than package/

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, like MMDet or MMCls.
4. The documentation has been modified accordingly, like docstring or example tutorials.

[codecov-commenter]

Codecov Report

Merging #68 (560e7f8) into main (0bd1f4d) will decrease coverage by 0.13%.
The diff coverage is 74.62%.

@@            Coverage Diff             @@
##             main      #68      +/-   ##
==========================================
- Coverage   64.08%   63.95%   -0.14%     
==========================================
  Files          21       21              
  Lines        1548     1559      +11     
  Branches      341      346       +5     
==========================================
+ Hits          992      997       +5     
+ Misses        429      428       -1     
- Partials      127      134       +7     

Flag	Coverage Δ
unittests	63.95% <74.62%> (-0.14%)	⬇️

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

Impacted Files	Coverage Δ
mim/commands/gridsearch.py	53.61% <33.33%> (-0.66%)	⬇️
mim/commands/train.py	45.88% <33.33%> (-1.11%)	⬇️
mim/commands/search.py	78.91% <60.00%> (-0.49%)	⬇️
mim/commands/run.py	63.51% <66.66%> (-0.26%)	⬇️
mim/commands/test.py	44.32% <66.66%> (+0.11%)	⬆️
mim/commands/download.py	88.46% <80.00%> (-1.74%)	⬇️
mim/commands/install.py	68.37% <89.47%> (-1.50%)	⬇️
mim/commands/list.py	82.14% <100.00%> (+7.94%)	⬆️
mim/utils/utils.py	78.94% <0.00%> (+2.02%)	⬆️

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[zhouzaida]

I am testing again in mmpose