[flink] Fix schema inference for multi partition Kafka topics

[ArnavBalyan]

Purpose

• Kafka table sync fails table creation when 1st partition has no cdc records, even when other partitions have records.
• Schema discovery reads only the 1st partition and fails with SchemaRetrievalException.
• Read records from all topic partitions so the schema is inferred from the first valid CDC record.

Tests

• UT

[JingsongLi]

+1