[DBZ-PGYB] Non-key columns should always be optional for replica identity CHANGE

[vaibhav-yb]

Problem

Suppose we create a table which has a non-key column which also has a constraint NOT NULL - when the connector will start and CDC service will send a RELATION message, the column will be marked as "required" since a NOT NULL column means that the value should be present.

But for a table with replica identity CHANGE the column will not be present in UPDATE operations if the column is not updated. This will violate the assumption of the column being marked as "required" since the value will not be present and the connector will end up throwing error of a similar format as:

org.apache.kafka.connect.errors.DataException: Invalid value: null used for required field: "name", schema type: STRUCT

Solution

This PR introduces a fix to the above problem by adding a check while decoding the relation message - the check essentially verifies that if the replica identity of the table is CHANGE then we explicitly mark the column as optional if it is a non key column.

[asrinivasanyb]

one test required