[IcebergIO AddFiles] Apply name mapping at commit time

[ahmedabu98]

Name mapping was getting applied at an earlier stage with high parallelism, causing locking due to multiple concurrent updateProperties requests.

Changed to only apply mapping at commit time, where parallelism is much lower (usually only 1)

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Summary of Changes

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This pull request optimizes the Iceberg IO connector by deferring the application of name mappings until the commit stage. By shifting this operation from a highly parallelized stage to a lower-parallelism commit stage, the change prevents unnecessary locking issues caused by concurrent property updates on the Iceberg table.

Highlights

• Performance Optimization: Moved the application of Iceberg name mapping from the table creation/loading phase to the commit phase to reduce concurrent updateProperties requests.
• Code Refactoring: Relocated the ensureNameMappingPresent method to the CommitManifestFilesDoFn class to support the new execution flow.

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[Abacn]

Thank you!

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