[Enhance] Enhance vis-pipeline tool

[Ezra-Yu]

Motivation

Enhance vis-pipeline tool refer to #561

Modification

1. add 'transformed' mode to vis transformed images.
2. modify 'pipeline' mode to vis intermediate images.
3. replace example pictures with url link, remove real pictures docs/_static/xxxx

BC-breaking (Optional)

the behave of mode 'pipeline' has changed.

Use cases (Optional)

1. 'transformed' mode

 python ./tools/visualizations/vis_pipeline.py ./configs/resnet/resnet50_8xb32_in1k.py --show --mode transformed

2. pipeline' mode

python ./tools/visualizations/vis_pipeline.py configs/swin_transformer/swin_base_224_b16x64_300e_imagenet.py --phase train --adaptive --mode pipeline --show

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

Merging #604 (7aeea42) into dev (9ee4157) will decrease coverage by 0.15%.
The diff coverage is n/a.

@@            Coverage Diff             @@
##              dev     #604      +/-   ##
==========================================
- Coverage   85.03%   84.88%   -0.16%     
==========================================
  Files         121      121              
  Lines        7393     7476      +83     
  Branches     1278     1288      +10     
==========================================
+ Hits         6287     6346      +59     
- Misses        916      942      +26     
+ Partials      190      188       -2     

Flag	Coverage Δ
unittests	84.80% <ø> (-0.24%)	⬇️

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

Impacted Files	Coverage Δ
mmcls/datasets/dataset_wrappers.py	70.58% <0.00%> (-21.08%)	⬇️
mmcls/models/losses/utils.py	56.25% <0.00%> (-1.33%)	⬇️
mmcls/datasets/utils.py	38.29% <0.00%> (ø)
mmcls/models/utils/attention.py	100.00% <0.00%> (ø)
mmcls/models/backbones/resnet.py	100.00% <0.00%> (ø)
mmcls/models/heads/stacked_head.py	100.00% <0.00%> (ø)
mmcls/models/backbones/regnet.py	98.05% <0.00%> (+0.01%)	⬆️
mmcls/models/backbones/shufflenet_v1.py	97.93% <0.00%> (+0.02%)	⬆️
mmcls/models/backbones/conformer.py	98.21% <0.00%> (+0.03%)	⬆️
mmcls/datasets/pipelines/transforms.py	88.27% <0.00%> (+0.04%)	⬆️
... and 17 more

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[yingfhu]

LGTM