[Feature] Add Halpe dataset

[jin-s13]

Motivation

Add Halpe dataset and related config files.

Modification

about halpe dataset

configs/_base_/datasets/halpe.py
mmpose/datasets/datasets/top_down/topdown_halpe_dataset.py
mmpose/datasets/datasets/__init__.py
mmpose/datasets/datasets/top_down/__init__.py

about configs

configs/wholebody/2d_kpt_sview_rgb_img/topdown_heatmap/halpe/hrnet_w32_halpe_256x192.py

small modifications to coco-wholebody to avoid possible errors.

mmpose/datasets/datasets/top_down/topdown_coco_wholebody_dataset.py

Checklist

Before PR:

• I have read and followed the workflow indicated in the CONTRIBUTING.md to create this PR.
• Pre-commit or linting tools indicated in CONTRIBUTING.md are used to fix the potential lint issues.
• Bug fixes are covered by unit tests, the case that causes the bug should be added in the unit tests.
• New functionalities are covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, including docstring or example tutorials.

After PR:

• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Merging #925 (8ad1d6e) into master (0069aff) will decrease coverage by 0.02%.
The diff coverage is 72.41%.

@@            Coverage Diff             @@
##           master     #925      +/-   ##
==========================================
- Coverage   82.82%   82.80%   -0.03%     
==========================================
  Files         189      190       +1     
  Lines       14146    14175      +29     
  Branches     2429     2433       +4     
==========================================
+ Hits        11716    11737      +21     
- Misses       1816     1821       +5     
- Partials      614      617       +3     

Flag	Coverage Δ
unittests	82.73% <72.41%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
mmpose/datasets/datasets/__init__.py	100.00% <ø> (ø)
...atasets/top_down/topdown_coco_wholebody_dataset.py	94.01% <0.00%> (-3.33%)	⬇️
...atasets/datasets/top_down/topdown_halpe_dataset.py	83.33% <83.33%> (ø)
mmpose/datasets/datasets/top_down/__init__.py	100.00% <100.00%> (ø)

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[luohao123]

@ly015 @jin-s13 Sorry for picking up this old PR here, but I noticed the above config are removed in latest mmpose.

May I ask where can I still get a workable (with latest mmpose) config file of Halpe dataset config file?