merge dev-1.x to main

Motivation

This PR is to add Human-Art dataset into MMPose.

Modification

The modifications are listed as follows:

• Add configs of Human-Art in the folder "configs" (The download links still need to be updated, at present, only td-hm_hrnet-w48_8xb32-210e_humanart-256x192 is trained. However, since Human-Art is a multi-scenario dataset that has the same keypoint definition as MSCOCO, users can use checkpoint trained on MSCOCO to test generalization ability of different models on Human-Art. And that is why I think giving different configs of Human-Art is necessary although the models are still not ready.)
• Edit documents of README.md, README_CN.md, docs/en/dataset_zoo/2d_body_keypoint.md, and docs/zh_cn/dataset_zoo/2d_body_keypoint.md (I find docs/zh_cn/dataset_zoo/2d_body_keypoint.md is in fact write in English hhh. So I follow previous doc add in English)
• Add Human-Art in mmpose/datasets/datasets/body/init.py, mmpose/datasets/datasets/body/humanart_dataset.py, configs/base/datasets/humanart.py, and configs/base/datasets/humanart_aic.py. Noted that the official usage of Human-Art is joint training with MSCOCO, so I did not write the training config in dataset combine mode (define two datasets and use one data config to combine them together), but simply use the json file we provided in our google drive, training_humanart_coco.json.

BC-breaking (Optional)

It does not.

Use cases (Optional)

It is the same with MSCOCO. E.G. Users can simply convert configs/body_2d_keypoint/topdown_heatmap/coco/td-hm_hrnet-w48_8xb32-210e_coco-256x192.py to configs/body_2d_keypoint/topdown_heatmap/humanart/td-hm_hrnet-w48_8xb32-210e_humanart-256x192.py for training and testing on Human-Art.

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 tests to ensure 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.