Custom PersistenceProvider - implement Snapshot logic

Create a PersistenceProvider OSGI service, which will replace the Akka’s PersistenceProvider. It needs to provide the same utilities via a similar API for:

• storing Snapshots from all Shards

• loading Snapshots

The service will be then injected into Shards. The goal is to make the transition from Akka to this service as seamless as possible.