tools: support setting float for qps

[rleungx]

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.

[codecov[bot]]

Codecov Report

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

Project coverage is 75.56%. Comparing base (39575d2) to head (6e2465b). Report is 2 commits behind head on master.

Additional details and impacted files

```diff @@ Coverage Diff @@ ## master #8787 +/- ## ========================================== - Coverage 75.69% 75.56% -0.14% ========================================== Files 461 461 Lines 72298 72304 +6 ========================================== - Hits 54729 54639 -90 - Misses 14078 14158 +80 - Partials 3491 3507 +16 ``` | [Flag](https://app.codecov.io/gh/tikv/pd/pull/8787/flags?src=pr&el=flags&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tikv) | Coverage Δ | | |---|---|---| | [unittests](https://app.codecov.io/gh/tikv/pd/pull/8787/flags?src=pr&el=flag&utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tikv) | `75.56% <63.63%> (-0.14%)` | :arrow_down: | Flags with carried forward coverage won't be shown. [Click here](https://docs.codecov.io/docs/carryforward-flags?utm_medium=referral&utm_source=github&utm_content=comment&utm_campaign=pr+comments&utm_term=tikv#carryforward-flags-in-the-pull-request-comment) to find out more.

[ti-chi-bot[bot]]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: lhy1024, okJiang

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Needs approval from an approver in each of these files: - ~~[OWNERS](https://github.com/tikv/pd/blob/master/OWNERS)~~ [lhy1024] Approvers can indicate their approval by writing `/approve` in a comment Approvers can cancel approval by writing `/approve cancel` in a comment

[ti-chi-bot[bot]]

[LGTM Timeline notifier]

Timeline:

• 2024-11-07 09:34:40.677513612 +0000 UTC m=+1119993.516669158: :ballot_box_with_check: agreed by okJiang.
• 2024-11-07 11:22:32.276467441 +0000 UTC m=+1126465.115622988: :ballot_box_with_check: agreed by lhy1024.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #8797.