Added expires_at to Status

• Added:
- expires_at key to Status

db/migrate/20200722190844_add_expires_at_to_status.rb

@@ -0,0 +1,6 @@
+class AddExpiresAtToStatus < ActiveRecord::Migration[5.2]
+  def change
+    add_column :statuses, :expires_at, :datetime
+    add_index :statuses, :expires_at
+  end
+end