misc(spark-job-iceberg-data-export)Assign correct NULL/NOT NULL type to columns in Iceberg Data Export S…

[nikitag55]

…chema

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Current behavior :

Currently, Iceberg Schema contains all columns as NULL type by default.

New behavior :

Assign correct NULL, NOT NULL to columns in Iceberg Schema for data export/

Changes to update the Iceberg Schema for Data Export are as follows:

• In conf file, update label-column-mapping to also specify for eg: workspace column to be NULL or NOT NULL and determine equivalent StructType true or false dynamically for creating the schema.

        "label-column-mapping": [
         "_ws_", "workspace", "NOT NULL",
         "_ns_", "namespace", "NOT NULL"
        ]

2. For all the other fixed columns in Iceberg Schema for data export, assign the correct NOT NULL type to some columns and also update the equivalent StructType defining the schema.