compact: add log for keyCompactions when finished compaction

[qsyqian]

add more log for debug #18509
Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[k8s-ci-robot]

Hi @qsyqian. Thanks for your PR.

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[codecov-commenter]

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Codecov Report

Attention: Patch coverage is 3.57143% with 27 lines in your changes missing coverage. Please review.

Project coverage is 68.82%. Comparing base (fe796ab) to head (453c1dc).
Report is 24 commits behind head on main.

❗ Current head 453c1dc differs from pull request most recent head 266270c

Please upload reports for the commit 266270c to get more accurate results.

Files with missing lines	Patch %	Lines
client/v3/kubernetes/client.go	0.00%	27 Missing ⚠️

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Additional details and impacted files

Files with missing lines	Coverage Δ
server/storage/mvcc/kvstore_compaction.go	100.00% <100.00%> (ø)
client/v3/kubernetes/client.go	0.00% <0.00%> (ø)

... and 26 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #18516      +/-   ##
==========================================
+ Coverage   68.77%   68.82%   +0.04%     
==========================================
  Files         420      420              
  Lines       35489    35471      -18     
==========================================
+ Hits        24407    24412       +5     
+ Misses       9650     9637      -13     
+ Partials     1432     1422      -10     

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[ahrtr]

/ok-to-test

[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: ahrtr, qsyqian

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[ahrtr]

@qsyqian please rebase this PR, which should be able to fix the govulncheck workflow failure.