FEATURE: Add descriptions on hover for hashtag search results (#19162)

Adds the description as a title="" attribute on the hashtag
autocomplete search items for tags, categories, and channels.
These descriptions can be seen by the user since they are
able to see the results that are returned by the search via
Guardian checks.

plugins/chat/lib/chat_channel_hashtag_data_source.rb

@@ -8,6 +8,7 @@ class Chat::ChatChannelHashtagDataSource
   def self.channel_to_hashtag_item(guardian, channel)
     HashtagAutocompleteService::HashtagItem.new.tap do |item|
       item.text = channel.title(guardian.user)
+      item.description = channel.description
       item.slug = channel.slug
       item.icon = icon
       item.relative_url = channel.relative_url