Upgrade to Hibernate Search 6.0.0.Beta9

TODO:

• Upgrade the Hibernate Search dependency (obviously); be warned the Lucene dependency is now 8.6.0
• Handle deprecations and breaking changes
• Simplify the configuration properties generated by Infinispan and passed to Hibernate Search; see here.
• Simplify the generation of IDs: org.hibernate.search.mapper.pojo.work.spi.PojoIndexer now allows passing the routing key explicitly (in our case, String.valueOf(segmentId)), so our custom implementation of RoutingKeyBridge (which relies on a hack) is no longer necessary.
• As a result of the previous item, we can also get rid of the hack that concatenates the segment ID to the document ID; see ISPN-12170.