[Feature] Add Maskfeat Support

[daidaiershidi]

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Motivation

Add maskfeat support.

Modification

Add MaskGenerator.
Add backbone of maskfeat.
Add head of maskfeat.
Add algorithms of maskfeat.
Add config of maskfeat.
Add Config of MaskFeat.
Update Readme of MaskFeat.

BC-breaking (Optional)

Does the modification introduce changes that break the backward compatibility of the downstream repositories?
If so, please describe how it breaks the compatibility and how the downstream projects should modify their code to keep compatibility with this PR.

Use cases (Optional)

If this PR introduces a new feature, it is better to list some use cases here and update the documentation.

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

Base: 72.48% // Head: 73.26% // Increases project coverage by +0.78% 🎉

Coverage data is based on head (fbf1e11) compared to base (6e6bec1).
Patch coverage: 89.51% of modified lines in pull request are covered.

❗ Current head fbf1e11 differs from pull request most recent head 2ee92b9. Consider uploading reports for the commit 2ee92b9 to get more accurate results

Additional details and impacted files

@@            Coverage Diff             @@
##              dev     #485      +/-   ##
==========================================
+ Coverage   72.48%   73.26%   +0.78%     
==========================================
  Files         121      125       +4     
  Lines        4765     4994     +229     
  Branches      763      788      +25     
==========================================
+ Hits         3454     3659     +205     
- Misses       1151     1167      +16     
- Partials      160      168       +8     

Flag	Coverage Δ
unittests	73.26% <89.51%> (+0.78%)	⬆️

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

Impacted Files	Coverage Δ
mmselfsup/datasets/pipelines/__init__.py	100.00% <ø> (ø)
mmselfsup/datasets/pipelines/transforms.py	83.33% <75.47%> (-1.87%)	⬇️
mmselfsup/models/heads/maskfeat_head.py	86.66% <86.66%> (ø)
mmselfsup/models/utils/hog_layer.py	93.22% <93.22%> (ø)
mmselfsup/models/backbones/maskfeat_vit.py	97.67% <97.67%> (ø)
mmselfsup/models/algorithms/__init__.py	100.00% <100.00%> (ø)
mmselfsup/models/algorithms/maskfeat.py	100.00% <100.00%> (ø)
mmselfsup/models/backbones/__init__.py	100.00% <100.00%> (ø)
mmselfsup/models/heads/__init__.py	100.00% <100.00%> (ø)

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[tonysy]

please add some comments for hog related parameters, to help the users.

[tonysy]

As inline comments

[tonysy]

How about using MaskFeatureMaskGenerator? @fangyixiao18

Suggested change

	class MaskfeatMaskGenerator(object):
	class MaskFeatMaskGenerator(object):

[fangyixiao18]

I think it is better to use MaskFeatMaskGenerator，consisting with algorithm name in our implementation

[tonysy]

Update the name and this pr could be merged.