The JPADefinition.DEPLOY_INSTANCE ResourceDefinition is not correct

Reusing JPADefinition for both the normal subsystem resource and the deployment subsystem resource causes some oddness.

The /deployment=*/subsystem=jpa resource should not have 'add' and 'remove' operations. A user invoking them would break things so they should not be present.

The 'default-datasource' and 'default-extended-persistence-inheritance' attributes don't make a lot of sense on the /deployment=*/subsystem=jpa resource either. But since they are part of the existing API and reading them doesn't do any harm, reads can be supported. Writes, no. And reads should be implemented by adding a step that reads the main subsystem value.