Enhance our svelte preprocessor

[quentinderoubaix]

Description
Following the introduction of our svelte preprocessor #730, we now have a preprocessor that helps add the necessary calls to ssrAttributes and classDirective to make sure we properly handle SSR.

We have in mind the following improvements however:

• make sure the preprocessor is not needed when using @agnos-ui/svelte-bootstrap (so transform those Svelte files before publishing). Svelte preprocessor improvements #739
• by default, run the preprocessor only on actions using a modifier |ssr
• support more options for the preprocessor (include / exclude blobs, option to choose the modifier...)