schedule: enable slow store scheduler by default in nextgen (#9949)

[ti-chi-bot]

This is an automated cherry-pick of #9949

What problem does this PR solve?

Issue Number: ref #9629

What is changed and how does it work?

Check List

Tests

• Unit test

Release note

None.

[rleungx]

/retest

[codecov]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 78.67%. Comparing base (13ab99f) to head (db9a4c0).
⚠️ Report is 3 commits behind head on release-nextgen-20251011.

Additional details and impacted files

@@                     Coverage Diff                      @@
##           release-nextgen-20251011   #10096      +/-   ##
============================================================
- Coverage                     78.68%   78.67%   -0.01%     
============================================================
  Files                           491      491              
  Lines                         66238    66242       +4     
============================================================
- Hits                          52117    52114       -3     
- Misses                        10354    10357       +3     
- Partials                       3767     3771       +4     

Flag	Coverage Δ
unittests	78.67% <100.00%> (-0.01%)	⬇️

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[rleungx]

/retest

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is NOT APPROVED

This pull-request has been approved by: lhy1024, rleungx
Once this PR has been reviewed and has the lgtm label, please assign benmeadowcroft for approval. For more information see the Code Review Process.
Please ensure that each of them provides their approval before proceeding.

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Details

Needs approval from an approver in each of these files:

• OWNERS [lhy1024,rleungx]
• pkg/schedule/config/OWNERS

Approvers can indicate their approval by writing /approve in a comment
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[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-12-19 06:31:09.510699808 +0000 UTC m=+1800214.324477380: ☑️ agreed by lhy1024.
• 2026-01-07 09:04:10.285138721 +0000 UTC m=+779406.103447153: ☑️ agreed by rleungx.