Add invite comments (#10465)

app/models/invite.rb

@@ -12,6 +12,7 @@
 #  created_at :datetime         not null
 #  updated_at :datetime         not null
 #  autofollow :boolean          default(FALSE), not null
+#  comment    :text
 #
 
 class Invite < ApplicationRecord
@@ -22,6 +23,8 @@ class Invite < ApplicationRecord
 
   scope :available, -> { where(expires_at: nil).or(where('expires_at >= ?', Time.now.utc)) }
 
+  validates :comment, length: { maximum: 420 }
+
   before_validation :set_code
 
   def valid_for_use?