[Proposal] New project to handle JSON serialization

The core SDK does not provide solutions for serialization of application domain objects, it only offers an interface. In order to enable applications to opt-in to specific serialization solutions, it might be better to expose as an optional project (similar to how it is done in Spring Boot).

This proposal is to create a new project for JSON serialization that apps can opt in and be extensible, so it can be configured to handle specific scenarios unique for each app. This package should be specific per vendor, which means a different JSON serializer should be done in a separate project.

This new project would also *not* be opinionated (but customizable) in how data types are serialized. Like DateTime, for example.

We can start with `dapr-jackson` project, where it uses the Jackson serializer. Possible names:
* `dapr-jackson`
* `dapr-serialization-jackson`
* `dapr-serialize-jackson`

## Open questions

* How would apps implement their own versioning logic on top of this serializer?

Inizia esaminando l’interfaccia di serializzazione del core SDK e l’approccio Spring Boot citato nella proposta. Determina come devono funzionare la personalizzazione opt-in e il versioning dell’applicazione, quindi definisci l’ambito e i criteri di completamento di un progetto dapr-jackson separato.

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