Add a user preference that can be used as a fallback for the sender authentication.

db/migrate/20220222184000_add_smspermittedsenders_to_preference.rb

@@ -0,0 +1,5 @@
+class AddSmspermittedsendersToPreference < ActiveRecord::Migration[5.2]
+  def change
+    add_column :preferences, :sms_permitted_senders, :string
+  end
+end

db/schema.rb

@@ -88,6 +88,7 @@ ActiveRecord::Schema.define(version: 2020_08_20_000743) do
     t.string "locale"
     t.integer "review_period", default: 14, null: false
     t.string "theme"
+    t.string "sms_permitted_senders"
     t.index ["user_id"], name: "index_preferences_on_user_id"
   end