chore: add merge_into_resize_parallel_threads settings

[JackTan25]

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Summary

if the machine has too many cores, maybe we will write too many small block, which cause high i/o cost.

Tests

• [ ] Unit Test
• [ ] Logic Test
• [ ] Benchmark Test
• [x] No Test - Explain why

Type of change

• [ ] Bug Fix (non-breaking change which fixes an issue)
• [ ] New Feature (non-breaking change which adds functionality)
• [ ] Breaking Change (fix or feature that could cause existing functionality not to work as expected)
• [ ] Documentation Update
• [ ] Refactoring
• [ ] Performance Improvement
• [x] Other (please describe):

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[github-actions[bot]]

Docker Image for PR

• tag: pr-15048-41ed2e7

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