add user and fix quote_post reference on posts/index

app/views/posts/_post.json.jbuilder

@@ -1,4 +1,6 @@
-json.extract! post, :id, :content, :user_id, :created_at, :updated_at
-json.url post_url(post, format: :json)
+json.extract! post, :id, :content, :created_at, :updated_at
 
-json.quoted_post(post.quoted_post)
+json.quoted_post(post.quoted_post, partial: 'posts/post', as: :post) if post.quoted_post
+json.user(post.user, partial: 'users/user', as: :user) if post.user
+
+json.url post_url(post, format: :json)