Introduce User#lower_email for case insensitive email lookups

app/models/user.rb

@@ -109,12 +109,19 @@ def self.lookup_by_email(email)
   # often we have the most probably user object onhand. so use that if possible
   def self.lookup_by_lower_email(email, cache = [])
     email = email.downcase
-    Array.wrap(cache).detect { |u| u.email.try(:downcase) == email } || find_by(['lower(email) = ?', email])
+    Array.wrap(cache).detect { |u| u.lower_email == email } || find_by(:lower_email => email)
   end
 
   singleton_class.send(:alias_method, :find_by_lower_email, :lookup_by_lower_email)
   Vmdb::Deprecation.deprecate_methods(singleton_class, :find_by_lower_email => :lookup_by_lower_email)
 
+  def lower_email
+    email&.downcase
+  end
+
+  virtual_attribute :lower_email, :string, :arel => ->(t) { t.grouping(t[:email].lower) }
+  hidden_attribute :lower_email
+
   def lower_userid
     userid&.downcase
   end