disttask: Change rand choose TiDB to round selection TiDB to be an executor (#43440)

[ti-chi-bot]

This is an automated cherry-pick of #43440

What problem does this PR solve?

Issue Number: close #43439

Problem Summary:

What is changed and how it works?

Change the random choose one of TiDB node to one specific subtask to round robin choose one TiDB to make subtasks could be evenly run on all available TiDB nodes.

Check List

Tests

• Unit test
• Integration test
• Manual test (add detailed scripts or steps below)
• No code

Side effects

• Performance regression: Consumes more CPU
• Performance regression: Consumes more Memory
• Breaking backward compatibility

Documentation

• Affects user behaviors
• Contains syntax changes
• Contains variable changes
• Contains experimental features
• Changes MySQL compatibility

Release note

Please refer to Release Notes Language Style Guide to write a quality release note.

None

[ti-chi-bot]

[REVIEW NOTIFICATION]

This pull request has been approved by:

• tangenta
• zimulala

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[Benjamin2037]

/retest

[zimulala]

LGTM

[Benjamin2037]

/merge

[ti-chi-bot]

This pull request has been accepted and is ready to merge.

Commit hash: ad292de