[Fix] rename custom_hooks_config to custom_hooks

[ly015]

Motivation

Change 'custom_hooks_config' to 'custom_hooks' in configs following the OpenMMLab convention. Compatibility to the old-style config is handled.

Modification

BC-breaking (Optional)

Use cases (Optional)

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.

[codecov]

Codecov Report

Merging #1427 (01574c0) into master (4f5ec97) will decrease coverage by 0.02%.
The diff coverage is 0.00%.

@@            Coverage Diff             @@
##           master    #1427      +/-   ##
==========================================
- Coverage   84.35%   84.32%   -0.03%     
==========================================
  Files         232      232              
  Lines       19279    19284       +5     
  Branches     3468     3470       +2     
==========================================
  Hits        16262    16262              
- Misses       2152     2157       +5     
  Partials      865      865              

Flag	Coverage Δ
unittests	84.26% <0.00%> (-0.03%)	⬇️

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

Impacted Files	Coverage Δ
mmpose/apis/train.py	21.05% <0.00%> (-1.49%)	⬇️

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