Add dynamic expression button for substitution line and new converter features

- Introduced a button to dynamically set the expression in the substitution line.
- The feature is available for converters of type "Odoo template", "Odoo template + Evaluation", and "Field".
- Added functionality to visualize how to define each converter, displaying a placeholder (example) for each converter type.
- The code has been designed to ease the integration of additional converters in the future.
- Refactored the code to improve performance and stability.