[Feature] Add retrieval mAP

[Ezra-Yu]

Motivation

1. Add retrieval mAP and unit tests relate to update metric mAP@k for image retrieval #980

Checklist

Before PR:

• Pre-commit or other linting tools are used to fix the potential lint issues.
• Bug fixes are fully covered by unit tests, the case that causes the bug should be added in the unit tests.
• The modification is covered by complete unit tests. If not, please add more unit test to ensure the correctness.
• The documentation has been modified accordingly, like docstring or example tutorials.

After PR:

• If the modification has potential influence on downstream or other related projects, this PR should be tested with those projects, like MMDet or MMSeg.
• CLA has been signed and all committers have signed the CLA in this PR.

[codecov]

Codecov Report

Patch coverage: 21.51% and project coverage change: -1.00 ⚠️

Comparison is base (f9dcae2) 68.16% compared to head (d892028) 67.17%.

❗ Current head d892028 differs from pull request most recent head 315311e. Consider uploading reports for the commit 315311e to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1552      +/-   ##
==========================================
- Coverage   68.16%   67.17%   -1.00%     
==========================================
  Files         295      303       +8     
  Lines       23372    23910     +538     
  Branches     3713     3786      +73     
==========================================
+ Hits        15932    16062     +130     
- Misses       6880     7283     +403     
- Partials      560      565       +5     

Flag	Coverage Δ
unittests	67.17% <21.51%> (-1.00%)	⬇️

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

Impacted Files	Coverage Δ
mmpretrain/apis/image_retrieval.py	21.42% <ø> (ø)
mmpretrain/datasets/__init__.py	70.27% <0.00%> (-4.02%)	⬇️
mmpretrain/datasets/gqa_dataset.py	0.00% <0.00%> (ø)
mmpretrain/datasets/nocaps.py	0.00% <0.00%> (ø)
mmpretrain/datasets/scienceqa.py	0.00% <ø> (ø)
mmpretrain/models/multimodal/__init__.py	40.00% <0.00%> (-4.45%)	⬇️
...retrain/models/multimodal/chinese_clip/__init__.py	0.00% <0.00%> (ø)
mmpretrain/models/multimodal/chinese_clip/bert.py	0.00% <0.00%> (ø)
...ain/models/multimodal/chinese_clip/chinese_clip.py	0.00% <0.00%> (ø)
mmpretrain/models/multimodal/chinese_clip/utils.py	0.00% <0.00%> (ø)
... and 13 more

... and 2 files with indirect coverage changes

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