FEATURE: the ability to search users by custom fields (#12762)

When the admin creates a new custom field they can specify if that field should be searchable or not.

That setting is taken into consideration for quick search results.

app/models/user_custom_field.rb

@@ -2,6 +2,8 @@
 
 class UserCustomField < ActiveRecord::Base
   belongs_to :user
+
+  scope :searchable, -> { joins("INNER JOIN user_fields ON user_fields.id = REPLACE(user_custom_fields.name, 'user_field_', '')::INTEGER AND user_fields.searchable IS TRUE AND user_custom_fields.name like 'user_field_%'") }
 end
 
 # == Schema Information