refactor: improve readability and maintainability of dataset handling

[TheMeinerLP]

Description

This small refactor helps maintainers and architects to improve maintainability and readability of the codebase.

Motivation

After I read the code, I found that some parts could be improved for better clarity and structure. This refactor aims to enhance the overall quality of the code.
This helps also to fix bugs faster and have a better software architecture and software design.

In order to enhance the quality of the code, it is recommended that the native features of NestJS and TypeScript be utilised. This approach is to be preferred over the implementation of a substantial if-else function within the code base.

My main idea was to use the layered architecture pattern to separate the concerns of different parts of the application. This helps to improve the maintainability and readability of the code.

Fixes

• No fixes directly, but it helps to improve the code quality.

Changes:

• Create datatypes for better readability
• Extract logic into extra service layer

Tests included

• Included for each change/fix?
• Passing?

Documentation

• swagger documentation updated (required for API changes)
• official documentation updated

official documentation info

[Junjiequan]

This refactor looks great. Is it still a work in progress or ready to be reviewd?

[TheMeinerLP]

I wanted to test this locally, but I'm happy to share it and resolve the merge conflict.