Feature: In-Memory (non-database, non-sql) DataManagers

**Is your feature request related to a problem? Please describe.**

Running hundreds of BPMN processes (sort of as 'lambda functions') per second against in-memory databases (H2 or HSQLDB) run into performance and locking problems.

**Describe the solution you'd like**

A faster, less database heavy option to execute BPMN processes, where the entities are not stored to SQL at all, but instead are kept in-memory in a (Concurrent) Map.

**Additional context**

The implementation does not need to provide full transaction support, as the intention is to run (mostly synchronous, though asynchronous must also work) short lived BPMN processes on it. If they fail in any non-expected way, the implementation is free to simply discard data (though creating a DeadLetter job would be good) while making sure the entities created within the failed process are also removed upon a critical failure.

La issue nomina DataManagers, ma non fornisce file, test o punti di ingresso da esaminare. Inizia individuando le implementazioni esistenti di DataManager e definisci come una map in memoria non-SQL gestisce i dati di processo sincroni e asincroni, la pulizia in caso di errore e la dichiarata mancanza di supporto completo alle transazioni.

Scritto dal modello di indicizzazione a partire dal testo della issue.