add default user signatures

db/migrate/20230922072041_create_user_configs.rb

@@ -0,0 +1,15 @@
+# frozen_string_literal: true
+
+class CreateUserConfigs < ActiveRecord::Migration[7.0]
+  def change
+    create_table :user_configs do |t|
+      t.references :user, null: false, foreign_key: true, index: true
+      t.string :key, null: false
+      t.text :value, null: false
+
+      t.index %i[user_id key], unique: true
+
+      t.timestamps
+    end
+  end
+end