[APIT-2658] Update the SQL statement in example

[channingdong]

Summary

Using our current statement example to insert data into Flink SQL database table will result in:

 Query schema: [order_id: STRING NOT NULL, customer_id: INT NOT NULL, product_id: STRING NOT NULL, price: DOUBLE NOT NULL]
│ Sink schema:  [key: BYTES, order_id: STRING, customer_id: INT, product_id: STRING, price: DOUBLE]

Reason being that the Sink schema has additional intrinsic key: BYTES, select everything from the sink schema will cause table mismatch and Flink statement creation failure.

Change

Update the SQL statement explicitly select fields for insert operation between query and sink schema.

JIRA reference

https://confluentinc.atlassian.net/browse/APIT-2658

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