💄(frontend) desaturate images system for generic theme

We want to desaturate the images system in the
generic theme to make them less colorful and more
in line with the overall theme.
We added a special class to the images
that need to be desaturated. Other property
then desaturated can be apply depending on the theme.

src/frontend/apps/impress/cunningham.ts

@@ -59,6 +59,7 @@ tokens.themes.default.components = {
     'la-gaufre': false,
     'home-proconnect': false,
     beta: false,
+    'image-system-filter': '',
   },
 };
 
@@ -228,6 +229,7 @@ const genericTheme = {
           },
         },
       },
+      'image-system-filter': 'saturate(0.2)',
     },
   },
 };