deprecate estargz

[imjasonh]

It's unclear whether this is practically taken advantage of at runtime, since it's relatively hard to run the estargz snapshotter.

There are some callers of this method out in the wild: https://github.com/search?type=code&auto_enroll=true&q=tarball.WithEstargz

If this is useful to others it may make sense to fork it into a separate repo that's capable of producing layers with estargz-optimized tarballs, but this probably isn't something we're going to maintain going forward.

This also removes the previously-hidden crane optimize command, and crane.Optimize, which had a big scary warning about it changing without warning. crane optimize only seems to be used in forks of Matt's mink repo, and crane.Optimize only seems to be used in forks of ggcr.

[codecov-commenter]

Codecov Report

Merging #1660 (bd0efb7) into main (1cb7e13) will increase coverage by 0.02%.
The diff coverage is 66.66%.

❗ Current head bd0efb7 differs from pull request most recent head c113d38. Consider uploading reports for the commit c113d38 to get more accurate results

@@            Coverage Diff             @@
##             main    #1660      +/-   ##
==========================================
+ Coverage   72.11%   72.13%   +0.02%     
==========================================
  Files         120      120              
  Lines        9814     9815       +1     
==========================================
+ Hits         7077     7080       +3     
+ Misses       2015     2014       -1     
+ Partials      722      721       -1     

Impacted Files	Coverage Δ
pkg/v1/tarball/layer.go	66.83% <0.00%> (-0.35%)	⬇️
pkg/crane/optimize.go	74.69% <100.00%> (ø)

... and 1 file with indirect coverage changes

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