Implement Instance Moderation Notes (#31529)

app/models/instance.rb

@@ -21,6 +21,7 @@ class Instance < ApplicationRecord
     belongs_to :unavailable_domain
 
     has_many :accounts, dependent: nil
+    has_many :moderation_notes, class_name: 'InstanceModerationNote', dependent: :destroy
   end
 
   scope :searchable, -> { where.not(domain: DomainBlock.select(:domain)) }