Add "why do you want to join" field to invite requests (#10524)

* Add "why do you want to join" field to invite requests

Fix #10512

* Remove unused translations

* Fix broken registrations when no invite request text is submitted

app/models/user_invite_request.rb

@@ -0,0 +1,17 @@
+# frozen_string_literal: true
+
+# == Schema Information
+#
+# Table name: user_invite_requests
+#
+#  id         :bigint(8)        not null, primary key
+#  user_id    :bigint(8)
+#  text       :text
+#  created_at :datetime         not null
+#  updated_at :datetime         not null
+#
+
+class UserInviteRequest < ApplicationRecord
+  belongs_to :user, inverse_of: :invite_request
+  validates :text, presence: true, length: { maximum: 420 }
+end