Added support for default categories and tags for external posts (#3417)

Based on discussion #3393.

---------

Signed-off-by: George Araújo <george.gcac@gmail.com>

_config.yml

@@ -122,13 +122,18 @@ disqus_shortname: al-folio # put your disqus shortname
 # External sources.
 # If you have blog posts published on medium.com or other external sources,
 # you can display them in your blog by adding a link to the RSS feed.
+# Optional: Set default categories and tags for posts from each source.
 external_sources:
   - name: medium.com
     rss_url: https://medium.com/@al-folio/feed
+    categories: [external-posts]
+    tags: [medium]
   - name: Google Blog
     posts:
       - url: https://blog.google/technology/ai/google-gemini-update-flash-ai-assistant-io-2024/
         published_date: 2024-05-14
+    categories: [external-posts]
+    tags: [google]
 
 # -----------------------------------------------------------------------------
 # Newsletter

_plugins/external-posts.rb

@@ -42,11 +42,11 @@ module ExternalPosts
           content: e.content,
           summary: e.summary,
           published: e.published
-        })
+        }, src)
       end
     end
 
-    def create_document(site, source_name, url, content)
+    def create_document(site, source_name, url, content, src = {})
       # check if title is composed only of whitespace or foreign characters
       if content[:title].gsub(/[^\w]/, '').strip.empty?
         # use the source name and last url segment as fallback
@@ -67,6 +67,15 @@ module ExternalPosts
       doc.data['description'] = content[:summary]
       doc.data['date'] = content[:published]
       doc.data['redirect'] = url
+      
+      # Apply default categories and tags from source configuration
+      if src['categories'] && src['categories'].is_a?(Array) && !src['categories'].empty?
+        doc.data['categories'] = src['categories']
+      end
+      if src['tags'] && src['tags'].is_a?(Array) && !src['tags'].empty?
+        doc.data['tags'] = src['tags']
+      end
+      
       doc.content = content[:content]
       site.collections['posts'].docs << doc
     end
@@ -76,7 +85,7 @@ module ExternalPosts
         puts "...fetching #{post['url']}"
         content = fetch_content_from_url(post['url'])
         content[:published] = parse_published_date(post['published_date'])
-        create_document(site, src['name'], post['url'], content)
+        create_document(site, src['name'], post['url'], content, src)
       end
     end