Add support for symbol link inside docker tar file

[yongxiu]

docker tar file containing multiple images will have symbol link for layer files to save space, this will read from the target file instead of the symbol link file

[codecov-commenter]

Codecov Report

Merging #987 (7a14a3f) into main (7b64627) will increase coverage by 0.01%.
The diff coverage is 100.00%.

❗ Current head 7a14a3f differs from pull request most recent head 4d5a3fd. Consider uploading reports for the commit 4d5a3fd to get more accurate results

@@            Coverage Diff             @@
##             main     #987      +/-   ##
==========================================
+ Coverage   74.60%   74.61%   +0.01%     
==========================================
  Files         107      107              
  Lines        5040     5043       +3     
==========================================
+ Hits         3760     3763       +3     
  Misses        725      725              
  Partials      555      555              

Impacted Files	Coverage Δ
pkg/v1/tarball/image.go	78.20% <100.00%> (+0.42%)	⬆️

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[jonjohnsonjr]

Overall lgtm other than that one question. Can you add a test as well?

There are some test tarball archives under https://github.com/google/go-containerregistry/tree/main/pkg/v1/tarball/testdata

[yongxiu]

Overall lgtm other than that one question. Can you add a test as well?

There are some test tarball archives under https://github.com/google/go-containerregistry/tree/main/pkg/v1/tarball/testdata

Added, please take another look, thanks.

[jonjohnsonjr]

Thanks!