Add missing metadata for Hibernate Reactive (needed for some collections mappings)

[radovanradic]

What does this PR do?

Adds missing metadata for Hibernate Reactive. Without this, when there are entities with @ManyToMany or @ElementCollection then following error was being thrown:

Caused by: org.hibernate.MappingException: Could not find appropriate constructor for org.hibernate.reactive.persister.collection.impl.ReactiveBasicCollectionPersister

Code sections where the PR accesses files, network, docker or some external service

• (example link to code section)
  The test was already using mysql community docker so I have not added anything extra.

Checklist before merging

• I have considered including reachability metadata directly in the library or the framework (see our contributing document)
• I am the original author of all content provided in the pull request, and I did not copy the content from any other source (see the tests section from our contributing document)
• For all tests where I am not the sole author, I have added a comment that proves I may publish them under the specified license (see the tests section from our contributing document)
• I have properly formatted metadata files (see our formatting guide)
• I have added thorough tests (see the tests section from our contributing document)
• I have filled all places where my pull request accesses files, network, docker, or any other external service (see the section above)