Use JPA as a default, but also support other systems (like NoSQL databases)

[stephanpelikan]

To validate VanillaBP-annotations in respect to BPMN-versioning all versions of BPMN-files need to be loaded by the adapter. Since Zeebe does not provide information about BPMN already deployed in the past, the adapter stores bundled BPMNs in a repository. They are loaded at startup next to the BPMN currently bundled to fullfill wiring and validation of all versions of BPMN loaded into Zeebe.

At the moment JPA-repositories are used to store and load this information. Since VanillaBP should not stick to JPA any Spring Data crud-repository should be fine. It is likely that many users will use JPA, so the auto-configuration should provide JPA repositories in case those crud-repositories are not provided by the business processing module.