api(cdc): fix create changefeed after scale-in pd (#12003)

[ti-chi-bot]

This is an automated cherry-pick of #12003

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.

[lidezhu]

/test pull-cdc-integration-mysql-test

[ti-chi-bot]

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This pull-request has been approved by: lidezhu

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[lidezhu]

/test all

[lidezhu]

/test pull-cdc-integration-kafka-test