Implement scale subresource on Pod owners

[SuperQ]

In order for PodDisruptionBudgets to work on various groups of Pods we need to implement the Scale subresource at the direct owner of the Pod.

Otherwise the PDB will return errors like:

status:
  conditions:
    - lastTransitionTime: "2026-04..."
      message: tikvs.core.pingcap.com does not implement the scale subresource
      reason: SyncFailed
      status: "False"
      type: DisruptionAllowed

Followup to #6213

Closes: #6901
Closes: #4221

[ti-chi-bot]

Hi @SuperQ. Thanks for your PR.

I'm waiting for a pingcap member to verify that this patch is reasonable to test. If it is, they should reply with /ok-to-test on its own line. Until that is done, I will not automatically test new commits in this PR, but the usual testing commands by org members will still work. Regular contributors should join the org to skip this step.

Once the patch is verified, the new status will be reflected by the ok-to-test label.

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[SuperQ]

👓 @liubog2008

[codecov-commenter]

Codecov Report

✅ All modified and coverable lines are covered by tests.
✅ Project coverage is 37.97%. Comparing base (fe02609) to head (decc403).

Additional details and impacted files

@@           Coverage Diff           @@
##             main    #6912   +/-   ##
=======================================
  Coverage   37.97%   37.97%           
=======================================
  Files         393      393           
  Lines       22605    22605           
=======================================
  Hits         8584     8584           
  Misses      14021    14021           

Flag	Coverage Δ
unittest	37.97% <ø> (ø)

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[liubog2008]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2026-05-25 04:38:47.624073109 +0000 UTC m=+240597.594238176: ☑️ agreed by liubog2008.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liubog2008

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[liubog2008]

/cherry-pick release-2.1

[ti-chi-bot]

@liubog2008: once the present PR merges, I will cherry-pick it on top of release-2.1 in the new PR and assign it to you.

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In response to this:

/cherry-pick release-2.1

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[ti-chi-bot]

@SuperQ: The following test failed, say /retest to rerun all failed tests or /retest-required to rerun all mandatory failed tests:

Test name	Commit	Details	Required	Rerun command
pull-e2e	decc403	link	true	/test pull-e2e

Full PR test history. Your PR dashboard.

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