Use I18n texts for image dimensions

This way it'll be possible to customize the text in languages not using
parenthesis or not using an "x" to define dimensions.

app/components/admin/site_customization/images/index_component.rb

@@ -20,6 +20,8 @@ class Admin::SiteCustomization::Images::IndexComponent < ApplicationComponent
     end
 
     def image_hint(image)
-      "(#{image.required_width}x#{image.required_height})"
+      t("admin.site_customization.images.index.dimensions",
+        width: image.required_width,
+        height: image.required_height)
     end
 end