scheduler: support changing batch for slow score scheduler

[rleungx]

What problem does this PR solve?

Issue Number: Close #xxx

What is changed and how does it work?

Check List

Tests

• Unit test

Release note

None.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

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[codecov]

Codecov Report

Attention: Patch coverage is 51.85185% with 13 lines in your changes missing coverage. Please review.

Project coverage is 76.29%. Comparing base (4d8009d) to head (84eb725).

Additional details and impacted files

@@            Coverage Diff             @@
##           master    #8888      +/-   ##
==========================================
+ Coverage   76.28%   76.29%   +0.01%     
==========================================
  Files         463      463              
  Lines       70474    70497      +23     
==========================================
+ Hits        53760    53785      +25     
+ Misses      13368    13362       -6     
- Partials     3346     3350       +4     

Flag	Coverage Δ
unittests	76.29% <51.85%> (+0.01%)	⬆️

Flags with carried forward coverage won't be shown. Click here to find out more.

[rleungx]

/retest

[rleungx]

/retest

[ti-chi-bot]

[FORMAT CHECKER NOTIFICATION]

Notice: To remove the do-not-merge/needs-linked-issue label, please provide the linked issue number on one line in the PR body, for example: Issue Number: close #123 or Issue Number: ref #456, multiple issues should use full syntax for each issue and be separated by a comma, like: Issue Number: close #123, ref #456.

_{📖 For more info, you can check the "Linking issues" section in the CONTRIBUTING.md.}