Breaking changes: Refactoring of new architecture

[Wh1isper]

Description

I will be designing the overall project architecture for the betterment of the project.

Until this PR is merged, all design and related documentation changes will be placed in here: https://synthetic-data-generator.readthedocs.io/en/breaking-refactoring/index.html

Motivation and Context

Motivation: https://synthetic-data-generator.readthedocs.io/en/breaking-refactoring/design/motivation.html

Architecture: https://synthetic-data-generator.readthedocs.io/en/breaking-refactoring/design/architecture.html

How has this been tested?

Types of changes

• Maintenance (no change in code, maintain the project's CI, docs, etc.)
• Bug fix (non-breaking change which fixes an issue)
• New feature (non-breaking change which adds functionality)
• Breaking change (fix or feature that would cause existing functionality to not work as expected)

Checklist:

• My code follows the code style of this project.
• My change requires a change to the documentation.
• I have updated the documentation accordingly.

[sweep-ai]

Apply Sweep Rules to your PR?

• Apply: All new business logic should have corresponding unit tests.
• Apply: Refactor large functions to be more modular.
• Apply: Add docstrings to all functions and file headers.

[Wh1isper]

I'll ping reviewers when it's ready.

Feel free to comment anytime, thanks!

[Wh1isper]

@MooooCat

This PR is long enough with the following modifications:

• rtd Documentation support: https://synthetic-data-generator.readthedocs.io/en/breaking-refactoring/index.html
• Added motivation and architecture documentation.
• Adjusted the code structure according to the new architecture
• Introduced DataConnector, DataProcessor and its plug-in system.
• Added Example and Test CIs for the new plugin system.
• Initialised Synthesizer

I'd like to request to merge this PR first for others who can benefit from the framework.

BTW, I prefer squash and merge for a clean commit tree

[MooooCat]

Glad to see more further results achieved under the new architecture.