Summary:
Add a test to verify that the enum oids are preserved after a YSQL major upgrade.
The test also verifies that when an enum type is used as a hash partition key,
rows remain correctly routed to the same partitions after the upgrade.
Jira: DB-16768

Test Plan: ./yb_build.sh release --cxx-test integration-tests_ysql_major_upgrade-test --gtest_filter YsqlMajorUpgradeTest.EnumTypes

Reviewers: telgersma

Reviewed By: telgersma

Subscribers: yql

Differential Revision: https://phorge.dev.yugabyte.com/D43872