MMPose V0.18.0 Release

Improvements

• Add automatic benchmark regression tools (#849, #880, #885) @liqikai9, @ly015
• Add copyright information and checking hook (#872)
• Add PR template (#875) @ly015
• Add citation information (#876) @ly015
• Add python3.9 in CI (#877, #883) @ly015
• Improve the quality of the documents (#845, #845, #848, #867, #870, #873, #896) @jin-s13, @ly015, @zhiqwang

Bug Fixes

• Fix redundant model weight loading in pytorch-to-onnx conversion (#850) @ly015
• Fix a bug in update_model_index.py that may cause pre-commit hook failure(#866) @ly015
• Fix a bug in interhand_3d_head (#890) @zengwang430521
• Fix pose tracking demo failure caused by out-of-date configs (#891)