Clarify documentation for Hibernate Search annotations

As part of the query docs, we should add reference about the Hibernate Search annotations such as SortableField.

https://docs.jboss.org/hibernate/search/5.11/api/org/hibernate/search/annotations/SortableField.html

Need to clarify what annotations are supported.

Additionally, need to clarify if there is any difference in using annotations directly in .proto schema files vs POJO.