[Feat] Add Visual Prompt Tuning

[Ezra-Yu]

Motivation

Visual Prompt Tuning

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: 70.27% and project coverage change: -3.33% ⚠️

Comparison is base (f9dcae2) 68.16% compared to head (12aa135) 64.84%.
Report is 78 commits behind head on dev.

❗ Current head 12aa135 differs from pull request most recent head 5ba8782. Consider uploading reports for the commit 5ba8782 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##              dev    #1769      +/-   ##
==========================================
- Coverage   68.16%   64.84%   -3.33%     
==========================================
  Files         295      363      +68     
  Lines       23372    26342    +2970     
  Branches     3713     4203     +490     
==========================================
+ Hits        15932    17082    +1150     
- Misses       6880     8639    +1759     
- Partials      560      621      +61     

Flag	Coverage Δ
unittests	64.84% <70.27%> (-3.33%)	⬇️

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

Files Changed	Coverage Δ
configs/_base_/datasets/imagenet_bs128_mbv3.py	100.00% <ø> (ø)
configs/_base_/datasets/imagenet_bs32.py	100.00% <ø> (ø)
...onfigs/_base_/datasets/imagenet_bs32_pil_resize.py	100.00% <ø> (ø)
configs/_base_/datasets/imagenet_bs64_swin_224.py	100.00% <ø> (ø)
configs/_base_/datasets/imagenet_bs64_swin_384.py	100.00% <ø> (ø)
mmpretrain/apis/feature_extractor.py	37.50% <0.00%> (ø)
mmpretrain/apis/image_caption.py	30.64% <0.00%> (ø)
mmpretrain/apis/image_retrieval.py	21.42% <0.00%> (ø)
mmpretrain/apis/visual_grounding.py	27.53% <0.00%> (ø)
mmpretrain/apis/visual_question_answering.py	25.67% <0.00%> (ø)
... and 7 more

... and 97 files with indirect coverage changes

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