changelog: add mixed rw performance evaluation backport

[ivanvc]

Add changelog entry from #19275

Please read https://github.com/etcd-io/etcd/blob/main/CONTRIBUTING.md#contribution-flow.

[codecov]

Codecov Report

All modified and coverable lines are covered by tests ✅

Project coverage is 68.82%. Comparing base (e757a45) to head (8a1a396).
Report is 26 commits behind head on main.

Additional details and impacted files

see 17 files with indirect coverage changes

@@            Coverage Diff             @@
##             main   #19291      +/-   ##
==========================================
- Coverage   68.86%   68.82%   -0.04%     
==========================================
  Files         420      420              
  Lines       35680    35680              
==========================================
- Hits        24571    24558      -13     
- Misses       9684     9696      +12     
- Partials     1425     1426       +1     

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[k8s-ci-robot]

[APPROVALNOTIFIER] This PR is APPROVED

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

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[ivanvc]

/cc @jmhbnz