add achievement management

db/migrate/20210815130352_create_completed_wow_achievements.rb

@@ -0,0 +1,11 @@
+class CreateCompletedWowAchievements < ActiveRecord::Migration[6.1]
+  def change
+    create_table :completed_wow_achievements do |t|
+      t.datetime :completed_timestamp
+      t.belongs_to :wow_character
+      t.belongs_to :wow_achievement
+
+      t.timestamps
+    end
+  end
+end