Adjust data model generation

[anzin]

Description (*)
I've adjusted data model generation process:

1. Interface creation was made optional.
2. If data model has not interface, the fields constants appears in the data model.
3. Adjusted getters and setters annotations for new behaviour.
4. For setters made return type void.
5. Added set and get null.
6. Added type for method parameters.
7. Added better description for annotations.

Contribution checklist (*)

• Pull request has a meaningful description of its purpose
• All commits are accompanied by meaningful commit messages
• All new or changed code is covered with integration/functional tests (if applicable)
• All automated tests passed successfully (all builds are green)

[DmitryFurs]

@coderimus @anzin it would be convenient to add an additional column named Is Nullable, and draw a checkbox in the cell, so that the code generator adds a nullable sign (?int, ?string and etc.) only to the explicitly specified fields, if the field is not nullable, then the typing must be strict (int, string and etc.).

[VitaliyBoyko]

Hi @DmitryFurs

What is the use case for such data models?
I believe it requires modifying the constructor to forbidе instantiating a class with empty fields.
This seems to be quite a specific request, not needed for most developers.

Maybe I miss something in terms of recent best practices 🤔
Let me know if so. Thank you!

[VitaliyBoyko]

By the way @anzin

We don't need to convert strings. AbstractDB returns them either way.

[VitaliyBoyko]

See my comment regarding strings.

[coderimus]

@anzin thank you for the provided update. QA passed. 👍