Feature Request: Add ability to extend TWIG files

[robertvy]

Hello,

I've been using the Mautic Advanced Templates Bundle and it's been a great help in expanding Mautic's email template capabilities. I appreciate the support for advanced Twig templating techniques that the bundle offers.

One feature of Twig that I find useful in other contexts is the extend function, which allows for a base "skeleton" template that has blocks that child templates can override. This provides a consistent layout across different emails or templates and promotes reusability of code.

I didn't see explicit mention in the documentation about support for the extend function in this bundle. I believe adding this functionality would benefit many users who want to further organize their templates and streamline their work.