Add remember-me function for sign-in

When checked, remember user for 2 weeks. Otherwise expire session after
30 minutes.

db/migrate/20230319101128_add_remember_created_at_to_users.rb

@@ -0,0 +1,6 @@
+class AddRememberCreatedAtToUsers < ActiveRecord::Migration[7.0]
+  def change
+    add_column :users, :remember_created_at, :datetime
+    add_column :users, :remember_token, :string
+  end
+end

db/schema.rb

@@ -10,7 +10,7 @@
 #
 # It's strongly recommended that you check this file into your version control system.
 
-ActiveRecord::Schema[7.0].define(version: 2023_02_23_115536) do
+ActiveRecord::Schema[7.0].define(version: 2023_03_19_101128) do
   create_table "donations", force: :cascade do |t|
     t.integer "user_id"
     t.integer "amount_sats"
@@ -57,6 +57,8 @@ ActiveRecord::Schema[7.0].define(version: 2023_02_23_115536) do
     t.text "ln_login_ciphertext"
     t.text "ln_password_ciphertext"
     t.string "ln_account"
+    t.datetime "remember_created_at"
+    t.string "remember_token"
     t.index ["email"], name: "index_users_on_email", unique: true
     t.index ["reset_password_token"], name: "index_users_on_reset_password_token", unique: true
   end