feat: CRUD operation for associated articles to current article (#4912)

db/migrate/20220608084622_add_associated_article_id.rb

@@ -0,0 +1,5 @@
+class AddAssociatedArticleId < ActiveRecord::Migration[6.1]
+  def change
+    add_reference :articles, :associated_article, foreign_key: { to_table: :articles }
+  end
+end

db/migrate/20220628124837_create_portal_members.rb

@@ -0,0 +1,12 @@
+class CreatePortalMembers < ActiveRecord::Migration[6.1]
+  def change
+    create_table :portal_members do |t|
+      t.bigint :portal_id
+      t.bigint :user_id
+      t.timestamps
+    end
+
+    add_index :portal_members, [:portal_id, :user_id], unique: true
+    add_index :portal_members, [:user_id, :portal_id], unique: true
+  end
+end