Issue #32280/ bug fix: WHERE segment with ON CONFLICT segment in INSERT throws exception

[omkar-shitole]

…ement of postgres

Fixes apache#32280

Changes proposed in this pull request:

• Added flow for whereSegment in onConflictKeyColumnSegment which was missing and required. The current flow is more intent on the on_duplicate of MySQL than on_conflict in Postgres which has been added in Postgres after Postgres 9.
• While using ON CONFLICT with INSERT INTO statement in Postgres it was throwing an exception (no value specified for parameter) as it was not able to set the flow for where statement present in the optOnConflict rule which was eventually failing to read parameter markers expressions and assignments present in whereSegment
• This fix resolves the error and ensures the successful execution of the INSERT INTO statement. The flow for ON DUPLICATE has not been removed or altered for now, as It may be useful for certain conditions of older versions of Postgres (and can be deprecated in future if no use case is observed for long)

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