Add description_html field to Category

(cherry picked from commit aa8f15f795)

src/invidious/helpers/extractors.cr

@@ -256,6 +256,9 @@ private class CategoryParser < ItemParser
       badges << {badge["style"].as_s, badge["label"].as_s}
     end
 
+    # Category description
+    description_html = item_contents["subtitle"]?.try { |desc| parse_content(desc) } || ""
+
     # Content parsing
     contents = [] of SearchItem
 
@@ -278,6 +281,7 @@ private class CategoryParser < ItemParser
     Category.new({
       title:                title,
       contents:             contents,
+      description_html:     description_html,
       browse_endpoint_data: browse_endpoint_data,
       badges:               badges,
     })

src/invidious/helpers/invidiousitems.cr

@@ -232,6 +232,7 @@ class Category
   property title : String
   property contents : Array(SearchItem)
   property browse_endpoint_data : String?
+  property description_html : String
   property badges : Array(Tuple(String, String))?
 
   def to_json(locale, json : JSON::Builder)