Better handling of dynamic forms

[n-bernat]

Currently, adding or removing a single field requires us to provide a list of all fields each time which results in more code and worse developer experience.

Adding a method that allows to (un)register a particular field would make it easier to manage forms, because it allows you to think in a more scoped way.

[pdenert]

Subforms have been created for this purpose. Have you tried using them? https://github.com/leancodepl/leancode_forms/blob/main/README.md#subforms