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.