Introduce extension points in the existing Java EE commands

JPA and REST commands are used in the Java EE addon but could perform differently when using another technology (like Spring Boot, for example).

Example:

JPA: In Spring Boot, there is no persistence.xml, but an application.properties file that contains the necessary information.

REST: Even though JAX-RS is not used, the generated REST endpoints would need extra annotations to perform correctly. This is accomplished now

Right now the JPASetupWizard for example delegates the action to a PersistenceOperations class directly. It would be nice if we could introduce some indirection (or even extract to a common addon) in the commands.execute() method.

One idea is to have a Command -> Facet -> Operations sequence, so other technologies (like Spring Boot) could reuse the same command by only implementing a different facet.