Generated Identity for example datasets

[mathemancer]

Related to #4071

This updates the SQL files for the example data sets to use GENERATED BY DEFAULT AS IDENTITY for the id columns, instead of SERIAL.

This doesn't solve #4071 for all cases, just in the case of our example data sets. I judged that this change should be made for said data sets regardless of how we want to solve #4071 in the long run.

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[Anish9901]

LGTM!