clarify the usage of certain standard config properties

[gavinking]

This pull request contains the following changes.

• The property jakarta.persistence.schema-generation.create-database-schemas is defined to be usable "in Java SE" as well is in Jakarta EE in the text of the spec (and that's useful) but it was not mentioned in the part of the spec which defines persistence.xml and so it was also missing from PersistenceConfiguration. I have added it where it was missing.
• The properties database-product-name and friends had already been promoted out of the schema generation section, but I forgot to add them to the section on persistence.xml. This is fixed here.
• The property jakarta.persistence.bean.manager was mentioned in one place in the text, but it was not in any of the lists of properties. I have added it to the list that includes the similar property jakarta.persistence.validation.factory. I have not added these to the list of persistence.xml properties, since apparently they're considered "integration-level", whatever that means.
• I have added some subsection headings to break this material up a bit better and make it easier to find stuff.
• I have proposed adding lists of configuration properties in inner interfaces of the Persistence class, as discussed in #863.