Add all-open option for Kotlin panache

[edeandrea]

The kotlin-maven-allopen plugin needs to be configured for entity classes.

The quickstart fails with this if this is not done:

2023-10-19 14:16:55,283 WARN  [io.qua.hib.orm.run.pro.ProxyDefinitions] (Quarkus Main Thread) Could not generate an enhanced proxy for entity 'org.acme.hibernate.orm.panache.Fruit' (class='org.acme.hibernate.orm.panache.Fruit') as it's final. Your application might perform better if we're allowed to extend it.
2023-10-19 14:16:55,742 WARN  [org.hib.met.int.EntityRepresentationStrategyPojoStandard] (JPA Startup Thread) HHH000305: Could not create proxy factory for:org.acme.hibernate.orm.panache.Fruit: org.hibernate.HibernateException: Getter methods of lazy classes cannot be final: org.acme.hibernate.orm.panache.Fruit#getName
	at org.hibernate.proxy.pojo.ProxyFactoryHelper.validateGetterSetterMethodProxyability(ProxyFactoryHelper.java:80)
	at org.hibernate.metamodel.internal.EntityRepresentationStrategyPojoStandard.createProxyFactory(EntityRepresentationStrategyPojoStandard.java:229)
	at org.hibernate.metamodel.internal.EntityRepresentationStrategyPojoStandard.<init>(EntityRepresentationStrategyPojoStandard.java:147)
	at org.hibernate.metamodel.internal.ManagedTypeRepresentationResolverStandard.resolveStrategy(ManagedTypeRepresentationResolverStandard.java:62)
	at org.hibernate.persister.entity.AbstractEntityPersister.<init>(AbstractEntityPersister.java:510)
	at org.hibernate.persister.entity.SingleTableEntityPersister.<init>(SingleTableEntityPersister.java:140)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance0(Native Method)
	at java.base/jdk.internal.reflect.NativeConstructorAccessorImpl.newInstance(NativeConstructorAccessorImpl.java:77)
	at java.base/jdk.internal.reflect.DelegatingConstructorAccessorImpl.newInstance(DelegatingConstructorAccessorImpl.java:45)
	at java.base/java.lang.reflect.Constructor.newInstanceWithCaller(Constructor.java:499)
	at java.base/java.lang.reflect.Constructor.newInstance(Constructor.java:480)
	at org.hibernate.persister.internal.PersisterFactoryImpl.createEntityPersister(PersisterFactoryImpl.java:92)
	at org.hibernate.persister.internal.PersisterFactoryImpl.createEntityPersister(PersisterFactoryImpl.java:75)
	at org.hibernate.metamodel.model.domain.internal.MappingMetamodelImpl.processBootEntities(MappingMetamodelImpl.java:247)
	at org.hibernate.metamodel.model.domain.internal.MappingMetamodelImpl.finishInitialization(MappingMetamodelImpl.java:185)
	at org.hibernate.internal.SessionFactoryImpl.initializeMappingModel(SessionFactoryImpl.java:321)
	at org.hibernate.internal.SessionFactoryImpl.<init>(SessionFactoryImpl.java:271)
	at io.quarkus.hibernate.orm.runtime.boot.FastBootEntityManagerFactoryBuilder.build(FastBootEntityManagerFactoryBuilder.java:84)
	at io.quarkus.hibernate.orm.runtime.FastBootHibernatePersistenceProvider.createEntityManagerFactory(FastBootHibernatePersistenceProvider.java:74)
	at jakarta.persistence.Persistence.createEntityManagerFactory(Persistence.java:80)
	at jakarta.persistence.Persistence.createEntityManagerFactory(Persistence.java:55)
	at io.quarkus.hibernate.orm.runtime.JPAConfig$LazyPersistenceUnit.get(JPAConfig.java:156)
	at io.quarkus.hibernate.orm.runtime.JPAConfig$1.run(JPAConfig.java:64)
	at java.base/java.lang.Thread.run(Thread.java:833)

Check list:

Your pull request:

• [ X ] targets the development branch
• [ X ] uses the 999-SNAPSHOT version of Quarkus
• [ X ] has tests (mvn clean test)
• [ X ] works in native (mvn clean package -Pnative)
• [ X ] has integration/native tests (mvn clean verify -Pnative)
• [ X ] makes sure the associated guide must not be updated
• [ X ] links the guide update pull request (if needed)
• [ X ] updates or creates the README.md file (with build and run instructions)
• [ X ] for new quickstart, is located in the directory component-quickstart
• [ X ] for new quickstart, is added to the root pom.xml and README.md

[quarkus-bot]

✔️ 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.