Upgrade to Hibernate ORM 6.6 / Search 7.2 / Reactive 2.4

[yrodiere]

Work in progress; we need releases of ORM, Search and Reactive before we can merge this. => Done

Here's what we will need to add to the migration guide:

== JPA / Hibernate ORM

=== Upgrade to Hibernate ORM 6.6

The Quarkus extensions for Hibernate ORM was upgraded to Hibernate ORM 6.6.

Hibernate ORM 6.6 is largely backwards-compatible with Hibernate ORM 6.5,
but a few checks have been tightened, so applications with incorrect configuration, mapping, or queries
may now throw exceptions where they used to experience only warnings and malfunctions. In particular:

* https://docs.jboss.org/hibernate/orm/6.6/migration-guide/migration-guide.html#merge-versioned-entity-when-row-is-deleted[Merging detects invalid creation attempts]:
passing to `merge` an entity with a `@GeneratedValue` identifier or a `@Version` property set to a non-null value
will now fail, whereas it used to (incorrectly) create the entity in database.
* https://docs.jboss.org/hibernate/orm/6.6/migration-guide/migration-guide.html#explicit-validation-of-annotated-class-types[Applying both `@MappedSuperclass` and `@Embeddable` on the same type is not longer allowed].

Some features are also now enabled by default to avoid unexpected -- and arguably error-prone -- behavior:

* https://docs.jboss.org/hibernate/orm/6.6/migration-guide/migration-guide.html#discriminator-based-embeddable-inheritance[Embeddables with `@Embeddable` annotated subtypes will now use discriminator-based inheritance by default].

Finally, behavior was altered in some cases to comply with the JPA specification:

* https://docs.jboss.org/hibernate/orm/6.6/migration-guide/migration-guide.html#criteria-jakartapersistencecriteriaexpressionasclass[`jakarta.persistence.criteria.Expression#as(Class)` is now an unchecked cast]: use `org.hibernate.query.criteria.JpaExpression#cast(Class)` to perform a checked cast.

See the https://docs.jboss.org/hibernate/orm/6.6/migration-guide/migration-guide.html[Hibernate ORM 6.6 migration guide] for more details.

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[gsmet]

I rebased, updated to the Final versions and force pushed.

[marko-bekhta]

thanks! 🎉

[gsmet]

I added the content written by Yoann to the migration guide.

[quarkus-bot]

Status for workflow Quarkus CI

This is the status report for running Quarkus CI on commit 09706de.

✅ The latest workflow run for the pull request has completed successfully.

It should be safe to merge provided you have a look at the other checks in the summary.

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