tools: support setting float for qps (#8787)

[ti-chi-bot]

This is an automated cherry-pick of #8787

What problem does this PR solve?

Issue Number: Ref #5739

What is changed and how does it work?

Check List

Tests

• Unit test

Release note

None.

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[codecov]

Codecov Report

Attention: Patch coverage is 63.63636% with 4 lines in your changes missing coverage. Please review.

Please upload report for BASE (release-8.5@051907b). Learn more about missing BASE report.

Additional details and impacted files

@@              Coverage Diff               @@
##             release-8.5    #8797   +/-   ##
==============================================
  Coverage               ?   75.58%           
==============================================
  Files                  ?      461           
  Lines                  ?    72287           
  Branches               ?        0           
==============================================
  Hits                   ?    54641           
  Misses                 ?    14146           
  Partials               ?     3500           

Flag	Coverage Δ
unittests	75.58% <63.63%> (?)

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[rleungx]

After discussion, we are not going to support it in v8.5.