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.

Add missing python-magic requirement for package