make remember configurable

config/initializers/devise.rb

@@ -187,7 +187,7 @@ Devise.setup do |config|
 
   # ==> Configuration for :rememberable
   # The time the user will be remembered without asking for credentials again.
-  config.remember_for = 2.years
+  config.remember_for = ENV.fetch('SESSION_REMEMBER_DAYS', '730').to_i.days
 
   # Invalidates all the remember me tokens when the user signs out.
   config.expire_all_remember_me_on_sign_out = true