Study possibility of integration with rich-model-forms-bundle

[Nek-]

Melodiia is providing some tooling to work with rich models and forms. This support is incomplete and need some tricks. In addition it's a little bit out of its scope.

The bundle rich-model-forms seems to address what we want to achieve. Melodiia may only provide API form types while the rich model support would be provided by this external bundle. This sounds really great.

Please notice also that all of this is connected to those Symfony issues:

• [Form] InvalidArgumentException while using type declaration in entity symfony/symfony#43509
• [META] Symfony 6 return type declarations symfony/symfony#43021