Add a feature gate to use PD's ready API as the readiness probe

[fgksgf]

What problem does this PR solve?

Port #6243
Close #6244

What is changed and how does it work?

Code changes

• Has Go code change
• Has CI related scripts change

Tests

• Unit test
• E2E test
• Manual test
• No code

Side effects

• Breaking backward compatibility
• Other side effects:

Related changes

• Need to cherry-pick to the release branch
• Need to update the documentation

Release Notes

Please refer to Release Notes Language Style Guide before writing the release note.

[github-actions]

/run-pull-e2e-kind-v2

[codecov-commenter]

Codecov Report

❌ Patch coverage is 36.36364% with 56 lines in your changes missing coverage. Please review.
✅ Project coverage is 45.98%. Comparing base (5ab4e8f) to head (743c507).
⚠️ Report is 108 commits behind head on feature/v2.

Additional details and impacted files

@@              Coverage Diff               @@
##           feature/v2    #6282      +/-   ##
==============================================
- Coverage       46.02%   45.98%   -0.04%     
==============================================
  Files             304      304              
  Lines           20054    20135      +81     
==============================================
+ Hits             9230     9260      +30     
- Misses          10824    10875      +51     

Flag	Coverage Δ
unittest	45.98% <36.36%> (-0.04%)	⬇️

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[github-actions]

/run-pull-e2e-kind-v2

[github-actions]

/run-pull-e2e-kind-v2

[github-actions]

/run-pull-e2e-kind-v2

[github-actions]

/run-pull-e2e-kind-v2

[liubog2008]

/test ?

[ti-chi-bot]

@liubog2008: The following commands are available to trigger optional jobs:

/test pull-e2e

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[liubog2008]

/test pull-e2e

[ti-chi-bot]

@fgksgf: 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	97aa107	link	false	/test pull-e2e

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[github-actions]

/run-pull-e2e-kind-v2

[github-actions]

/run-pull-e2e-kind-v2

[github-actions]

/run-pull-e2e-kind-v2

[github-actions]

/run-pull-e2e-kind-v2

[github-actions]

/run-pull-e2e-kind-v2

[fgksgf]

/run-pull-e2e-kind-v2

[liubog2008]

/lgtm

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-07-09 12:07:06.831140005 +0000 UTC m=+2087879.554318988: ☑️ agreed by liubog2008.

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: liubog2008

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