fix: prevent DataFusion RepartitionExec insertion into IcebergCommitExec

[sgrebnov]

Which issue does this PR close?

PR adds required_input_distribution setting for IcebergWriteExec to ensure DataFusion coalesces input partitions automatically before commit, fixing partitioning issues in Iceberg write operations (partial writes). Closes spiceai/spiceai#7407

Despite the following code, w/o proper IcebergWriteExec settings DF optimizer rewrites this resulting in the following physical plan as a result sometimes only first partition is handled.

Physical plan: 
IcebergCommitExec: table=test_namespace.test_table_partitioning
  RepartitionExec: partitioning=RoundRobinBatch(8), input_partitions=3
    IcebergWriteExec: table=test_namespace.test_table_partitioning
      DataSourceExec: partitions=3, partition_sizes=[1, 1, 1]

https://github.com/spiceai/iceberg-rust/blob/spiceai-0.7.0-rc1/crates/integrations/datafusion/src/table/mod.rs#L212-L225

        let write_plan = Arc::new(IcebergWriteExec::new(
            self.table.clone(),
            input,
            self.schema.clone(),
        ));

        // Merge the outputs of write_plan into one so we can commit all files together
        let coalesce_partitions = Arc::new(CoalescePartitionsExec::new(write_plan));

        Ok(Arc::new(IcebergCommitExec::new(
            self.table.clone(),
            catalog,
            coalesce_partitions,
            self.schema.clone(),
        )))

After

IcebergCommitExec: table=test_namespace.test_table
  CoalescePartitionsExec
    IcebergWriteExec: table=test_namespace.test_table
      DataSourceExec: partitions=3, partition_sizes=[1, 1, 1]";

What changes are included in this PR?

Are these changes tested?

[sgrebnov]

Upstream PR created: apache#1723