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

config/locales/en/admin.yml

@@ -1615,6 +1615,7 @@ en:
             subnavigation_right: Main Navigation Right
       images:
         index:
+          dimensions: "(%{width}x%{height})"
           title: Custom images
           update: Update
           image: Image

config/locales/es/admin.yml

@@ -1615,6 +1615,7 @@ es:
             subnavigation_right: Navegación principal derecha
       images:
         index:
+          dimensions: "(%{width}x%{height})"
           title: Personalizar imágenes
           update: Actualizar
           image: Imagen