FEATURE: Add dark mode option for category logos (#18460)

Adds a new upload field for a second dark mode category logo. 
This alternative will be used when the browser is in dark mode (similar to the global site setting for a dark logo).

lib/tasks/site.rake

@@ -210,6 +210,7 @@ task 'site:export_structure', [:zip_path] => :environment do |task, args|
       sort_order: c.sort_order,
       sort_ascending: c.sort_ascending,
       uploaded_logo_id: data.set_upload(c.uploaded_logo_id),
+      uploaded_logo_dark_id: data.set_upload(c.uploaded_logo_dark_id),
       uploaded_background_id: data.set_upload(c.uploaded_background_id),
       topic_featured_link_allowed: c.topic_featured_link_allowed,
       all_topics_wiki: c.all_topics_wiki,

lib/tasks/uploads.rake

@@ -905,6 +905,7 @@ def analyze_missing_s3
       [:user_profiles, :profile_background_upload_id],
       [:user_profiles, :card_background_upload_id],
       [:categories, :uploaded_logo_id],
+      [:categories, :uploaded_logo_dark_id],
       [:categories, :uploaded_background_id],
       [:custom_emojis, :upload_id],
       [:theme_fields, :upload_id],

lib/upload_security.rb

@@ -29,6 +29,7 @@ class UploadSecurity
     profile_background
     card_background
     category_logo
+    category_logo_dark
     category_background
     group_flair
     badge_image