private registry support

[fenio]

closes #58

[codecov]

Codecov Report

Attention: Patch coverage is 37.66234% with 48 lines in your changes missing coverage. Please review.

Project coverage is 24.17%. Comparing base (f5f155e) to head (64d856b).

Files with missing lines	Patch %	Lines
pkg/plugin/mount.go	44.61%	33 Missing and 3 partials ⚠️
cmd/plugin/cli/mount.go	0.00%	12 Missing ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main      #71      +/-   ##
==========================================
- Coverage   27.54%   24.17%   -3.38%     
==========================================
  Files           7        7              
  Lines         599      633      +34     
==========================================
- Hits          165      153      -12     
- Misses        426      471      +45     
- Partials        8        9       +1     

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