Allow AttributeConverter's for non java.util collections and containers

It doesn't seem to be possible to use Vavr collections and optionals (as well as Guava optionals) with the SDK. Vavr is a popular project and well supported in the OSS ecosystem (JDBI provides an integration, there are modules for AssertJ and Jackson, Spring MVC and Spring Data supports Vavr types OOTB...)

The `AttributeConverter` interface requires `EnhancedType` for classes it converts. And `EnhancedType` has an API that permits only `java.util.Set/List/Optional`.

## Describe the Feature
Allow building `AttributeConverter` for arbitrary types, or implement support for Vavr https://www.vavr.io collections

## Additional Context
Initially I tried writing a converter using `ListAttributeConverter` and `SetAttributeConvert` as examples, didn't succeed and now I have a layer of DTOs + boilerplate converters for every domain entity.

Inizia leggendo AttributeConverter e EnhancedType, quindi confronta gli esempi menzionati di ListAttributeConverter e SetAttributeConvert. Determina se i tipi di converter arbitrari o le collezioni Vavr rientrano nell’ambito previsto; il lavoro è completato quando esiste un percorso supportato per i tipi non-java.util richiesti, senza DTO e converter boilerplate.

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