Fix 10593 -- add --keep option to experiment remove

[rmic]

• ❗ I have followed the Contributing to DVC checklist.

• 📖 If this PR requires documentation updates, I have created a separate PR (or issue, at least) in dvc.org and linked it here : Update documentation for fix #10593 dvc.org#5325

Addresses #10593 : added a --keep flag on dvc exp remove to be able to keep only (instead of delete) the last n experiments.

[codecov]

Codecov Report

Attention: Patch coverage is 98.21429% with 2 lines in your changes missing coverage. Please review.

Project coverage is 86.00%. Comparing base (2431ec6) to head (8155b3c).
Report is 5 commits behind head on main.

Files with missing lines	Patch %	Lines
dvc/repo/experiments/remove.py	83.33%	1 Missing and 1 partial ⚠️

Additional details and impacted files

@@            Coverage Diff             @@
##             main   iterative/dvc#10632      +/-   ##
==========================================
- Coverage   90.68%   86.00%   -4.68%     
==========================================
  Files         504      482      -22     
  Lines       39795    36803    -2992     
  Branches     3141     2761     -380     
==========================================
- Hits        36087    31654    -4433     
- Misses       3042     4544    +1502     
+ Partials      666      605      -61     

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