nydusify: refactor check subcommand

[imeoer]

• allow either the source or target to be an OCI or nydus image;
• improve output directory and log format;

Relevant Issue (if applicable)

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Details

Please describe the details of PullRequest.

Types of changes

What types of changes does your PullRequest introduce? Put an x in all the boxes that apply:

• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to change)
• Documentation Update (if none of the other choices apply)

Checklist

Go over all the following points, and put an x in all the boxes that apply.

• I have updated the documentation accordingly.
• I have added tests to cover my changes.

[codecov]

Codecov Report

Attention: Patch coverage is 15.38462% with 242 lines in your changes missing coverage. Please review.

Project coverage is 59.95%. Comparing base (375f55f) to head (a09f536).
Report is 1 commits behind head on master.

Files with missing lines	Patch %	Lines
contrib/nydusify/pkg/checker/rule/filesystem.go	0.00%	150 Missing ⚠️
contrib/nydusify/pkg/utils/utils.go	0.00%	30 Missing ⚠️
contrib/nydusify/pkg/checker/rule/bootstrap.go	0.00%	25 Missing ⚠️
contrib/nydusify/pkg/checker/rule/manifest.go	67.69%	13 Missing and 8 partials ⚠️
contrib/nydusify/cmd/nydusify.go	0.00%	16 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #1652      +/-   ##
==========================================
- Coverage   60.10%   59.95%   -0.16%     
==========================================
  Files         147      147              
  Lines       49513    49640     +127     
  Branches    46994    46994              
==========================================
- Hits        29762    29760       -2     
- Misses      17970    18094     +124     
- Partials     1781     1786       +5     

Files with missing lines	Coverage Δ
contrib/nydusify/cmd/nydusify.go	13.89% <0.00%> (-0.17%)	⬇️
contrib/nydusify/pkg/checker/rule/manifest.go	69.87% <67.69%> (-14.18%)	⬇️
contrib/nydusify/pkg/checker/rule/bootstrap.go	0.00% <0.00%> (ø)
contrib/nydusify/pkg/utils/utils.go	58.38% <0.00%> (-14.72%)	⬇️
contrib/nydusify/pkg/checker/rule/filesystem.go	0.00% <0.00%> (ø)

... and 2 files with indirect coverage changes