added stats to prune command, fixes #9262

[ThomasWaldmann]

-v / --info displays archive counts (total, kept, pruned).

fwd port of #9271.

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 76.48%. Comparing base (be42fdf) to head (b2fe60c).
⚠️ Report is 3 commits behind head on master.
✅ All tests successful. No failed tests found.

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #9420      +/-   ##
==========================================
- Coverage   76.48%   76.48%   -0.01%     
==========================================
  Files          85       85              
  Lines       14804    14806       +2     
  Branches     2213     2213              
==========================================
+ Hits        11323    11324       +1     
  Misses       2803     2803              
- Partials      678      679       +1     

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