CP to 2.77: Addfiles wiring provider (#40150)

[claudevdm]

• AddFiles: wire the schema pre-pass behind a Wait.on gate (batch)

AddFiles gets a ninth constructor argument, SchemaEvolutionConfig

With options set, the topology becomes

paths -> ReadFooterSchema -> CollectDistinctSchemas -> CommitSchemaOnce
|
paths -> Wait.on(signal) -> ConvertToDataFile -> ... (unchanged)

so no path reaches ConvertToDataFile until the schema commit has landed.

• IcebergAddFiles provider: schema_evolution_options, required_columns, incompatible_schema_handling, unverifiable_file_handling

Exposes the pre-pass through the iceberg_add_files SchemaTransform and Beam YAML:

• type: WriteToIceberg (transform: IcebergAddFiles in YAML)
  config:
  table: db.sales
  schema_evolution_options: [ALLOW_FIELD_ADDITION, ALLOW_TYPE_PROMOTION]
  required_columns: [id]
  incompatible_schema_handling: ROUTE_TO_ERRORS

• trigger tests

• simplify arg

• tests

• fixes

• changes

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[claudevdm]

@Amar3tto can you PTAL?

[github-actions]

Assigning reviewers:

R: @tvalentyn for label python.
R: @ahmedabu98 for label java.
R: @derrickaw for label yaml.
R: @ahmedabu98 for label iceberg.

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