api(cdc): fix create changefeed after scale-in pd

[lidezhu]

What problem does this PR solve?

Issue Number: close #12004

What is changed and how it works?

When the api request doesn't contain any pd address, we previously use the old pd address to create a new pd client.
If the old pd address are all scaled-in, the newly created pd client cannot connect to the upstream.
To fix this problem, in this case we should use pd client in the default upstream of the capture which can manage pd scale-in/scale-out internally.

Check List

Tests

• Unit test
• Manual test (add detailed scripts or steps below)

1. Deploy a cluster with 3 pds;
2. Scale out 3 new pds;
3. Transfer pd leader;
4. Scale in 3 old pds;
5. Create changefeed;

Questions

Will it cause performance regression or break compatibility?

Do you need to update user documentation, design documentation or monitoring documentation?

Release note

Fix create changefeed after scale in pds in some scenarios.

[codecov]

Codecov Report

Attention: Patch coverage is 78.40909% with 19 lines in your changes missing coverage. Please review.

Project coverage is 55.3902%. Comparing base (fa5baad) to head (bc53da5).
Report is 5 commits behind head on master.

✅ All tests successful. No failed tests found.

Additional details and impacted files

Components	Coverage Δ
cdc	59.8619% <78.4090%> (+0.1328%)	⬆️
dm	50.1708% <ø> (+0.0268%)	⬆️
engine	53.2505% <ø> (+0.0564%)	⬆️

Flag	Coverage Δ
unit	55.3902% <78.4090%> (+0.1100%)	⬆️

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

@@               Coverage Diff                @@
##             master     #12003        +/-   ##
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+ Coverage   55.2801%   55.3902%   +0.1100%     
================================================
  Files          1028       1028                
  Lines        142724     142991       +267     
================================================
+ Hits          78898      79203       +305     
+ Misses        58052      58000        -52     
- Partials       5774       5788        +14     

[ti-chi-bot]

[LGTM Timeline notifier]

Timeline:

• 2025-01-20 03:40:57.796001755 +0000 UTC m=+65785.126921153: ☑️ agreed by asddongmen.
• 2025-01-21 02:23:17.464513999 +0000 UTC m=+147524.795433403: ☑️ agreed by hongyunyan.

[lidezhu]

@yudongusa PTAL

[lidezhu]

/assign

[ti-chi-bot]

[APPROVALNOTIFIER] This PR is APPROVED

This pull-request has been approved by: asddongmen, hongyunyan, yudongusa

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Needs approval from an approver in each of these files:

• OWNERS [asddongmen,hongyunyan]
• cdc/api/v2/OWNERS [yudongusa]

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[lidezhu]

/run-cherry-picker

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.1: #12028.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.5: #12029.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-6.5: #12030.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-7.1: #12031.

[ti-chi-bot]

In response to a cherrypick label: new pull request created to branch release-8.5: #12032.