Introduce theming to reduce reliance on Custom CSS

[GrowwithNaveen]

Problem Description:
Currently, extensive custom CSS is required to achieve specific design themes within ToolJet applications. This creates several challenges:

1. Increased Development Time: Developers spend significant time writing and maintaining custom CSS, hindering rapid development.
2. Inconsistent Design: Maintaining consistent UI across applications becomes difficult with scattered CSS code.
3. Steeper Learning Curve: New developers require a deeper understanding of the codebase to implement design changes.

Solution in pipeline:
Pre-built Theme Components:

1. Create a library of pre-built, themable components
2. These components would be built with design tokens that inherit styles from the active theme.
3. This reduces the need for developers to write custom CSS for common UI elements.

Notes:

1. This solution should be implemented incrementally, focusing on the most commonly used theming options in the first phase.
2. Consider offering the ability to import and export themes for easy sharing and collaboration.
3. Explore integrating with popular design systems to leverage existing pre-built components and styles.