feat: Email signature API support (#3874)

app/models/user.rb

@@ -2,33 +2,35 @@
 #
 # Table name: users
 #
-#  id                     :integer          not null, primary key
-#  availability           :integer          default("online")
-#  confirmation_sent_at   :datetime
-#  confirmation_token     :string
-#  confirmed_at           :datetime
-#  current_sign_in_at     :datetime
-#  current_sign_in_ip     :string
-#  custom_attributes      :jsonb
-#  display_name           :string
-#  email                  :string
-#  encrypted_password     :string           default(""), not null
-#  last_sign_in_at        :datetime
-#  last_sign_in_ip        :string
-#  name                   :string           not null
-#  provider               :string           default("email"), not null
-#  pubsub_token           :string
-#  remember_created_at    :datetime
-#  reset_password_sent_at :datetime
-#  reset_password_token   :string
-#  sign_in_count          :integer          default(0), not null
-#  tokens                 :json
-#  type                   :string
-#  ui_settings            :jsonb
-#  uid                    :string           default(""), not null
-#  unconfirmed_email      :string
-#  created_at             :datetime         not null
-#  updated_at             :datetime         not null
+#  id                        :integer          not null, primary key
+#  availability              :integer          default("online")
+#  confirmation_sent_at      :datetime
+#  confirmation_token        :string
+#  confirmed_at              :datetime
+#  current_sign_in_at        :datetime
+#  current_sign_in_ip        :string
+#  custom_attributes         :jsonb
+#  display_name              :string
+#  email                     :string
+#  encrypted_password        :string           default(""), not null
+#  last_sign_in_at           :datetime
+#  last_sign_in_ip           :string
+#  message_signature         :text
+#  message_signature_enabled :boolean          default(FALSE), not null
+#  name                      :string           not null
+#  provider                  :string           default("email"), not null
+#  pubsub_token              :string
+#  remember_created_at       :datetime
+#  reset_password_sent_at    :datetime
+#  reset_password_token      :string
+#  sign_in_count             :integer          default(0), not null
+#  tokens                    :json
+#  type                      :string
+#  ui_settings               :jsonb
+#  uid                       :string           default(""), not null
+#  unconfirmed_email         :string
+#  created_at                :datetime         not null
+#  updated_at                :datetime         not null
 #
 # Indexes
 #