Improve IcebergCommitExec to correctly populate properties/schema

[sgrebnov]

Which issue does this PR close?

PR fixes schema mismatch errors (similar to the example shown below) when using IcebergCommitExec with DataFusion. This occurs when IcebergCommitExec is not the top-level plan but is instead wrapped as the input to another plan node, for example when added by a custom optimization rule (cache invalidation step for example).

An internal error occurred. Internal error: PhysicalOptimizer rule 'OutputRequirements' failed. Schema mismatch. Expected original schema: Schema { fields: [Field { name: "count", data_type: UInt64, nullable: false, dict_id: 0, dict_is_ordered: false, metadata: {} }], metadata: {} }, got new schema: Schema { fields: [Field { name: "r_regionkey", data_type: Int32, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {"PARQUET:field_id": "1"} }, Field { name: "r_name", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {"PARQUET:field_id": "2"} }, Field { name: "r_comment", data_type: Utf8, nullable: true, dict_id: 0, dict_is_ordered: false, metadata: {"PARQUET:field_id": "3"} }], metadata: {} }.
This issue was likely caused by a bug in DataFusion's code. Please help us to resolve this by filing a bug report in our issue tracker: https://github.com/apache/datafusion/issues

What changes are included in this PR?

PR updates compute_properties logic to use target (output) schema instead of input schema. Below is example DataFusion DataSinkExec implementation demonstrating that properties must be created based on target schema, not input.

https://github.com/apache/datafusion/blob/4eacb6046773b759dae0b3d801fe8cb1c6b65c0f/datafusion/datasource/src/sink.rs#L101C1-L117C6

impl DataSinkExec {
    /// Create a plan to write to `sink`
    pub fn new(
        input: Arc<dyn ExecutionPlan>,
        sink: Arc<dyn DataSink>,
        sort_order: Option<LexRequirement>,
    ) -> Self {
        let count_schema = make_count_schema();
        let cache = Self::create_schema(&input, count_schema);
        Self {
            input,
            sink,
            count_schema: make_count_schema(),
            sort_order,
            cache,
        }
    }
....

    fn properties(&self) -> &PlanProperties {
        &self.cache
    }

Are these changes tested?

Tested manually, expanded existing test to verify output schema, tested as part of Spice Iceberg write automated tests

[CTTY]

LGTM, thanks for the fix!

I'm questioning if we actually need to store table schema in the IcebergCommitExec. Commit node should be taking data files and rows count, and output only the sum of rows count, and don't really need to be aware of table schema. But either way, this can be done in a separate PR and should not block this fix