add default user signatures

app/models/user_config.rb

@@ -0,0 +1,29 @@
+# frozen_string_literal: true
+
+# == Schema Information
+#
+# Table name: user_configs
+#
+#  id         :bigint           not null, primary key
+#  key        :string           not null
+#  value      :text             not null
+#  created_at :datetime         not null
+#  updated_at :datetime         not null
+#  user_id    :bigint           not null
+#
+# Indexes
+#
+#  index_user_configs_on_user_id          (user_id)
+#  index_user_configs_on_user_id_and_key  (user_id,key) UNIQUE
+#
+# Foreign Keys
+#
+#  fk_rails_...  (user_id => users.id)
+#
+class UserConfig < ApplicationRecord
+  SIGNATURE_KEY = 'signature'
+
+  belongs_to :user
+
+  serialize :value, JSON
+end