JDBC based implementation of AppFileSystem

[sylvlecl]

• Do you want to request a feature or report a bug?

Feature: add a JDBC-based implementation of the AFS interface (AppStorage in particular).

• What is the current behavior?

Only MapDB implementation of AFS is provided.

• If the current behavior is a bug, please provide the steps to reproduce and if possible a minimal demo of the problem

• What is the expected behavior?

We want to be able to use a relational database as the storage for AFS. As much as possible, the implementation should be vendor-independent. It should rely on a plain JDBC connection and not JPA, in order to keep it a "2 mayers" abstraction, not 3 layers.

• What is the motivation / use case for changing the behavior?

No "production ready" implementation of AFS is available in powsybl-core.

• Please tell us about your environment:

• Other information (e.g. detailed explanation, stacktraces, related issues, suggestions how to fix, links for us to have context, eg. stackoverflow, gitter, etc)