def add_model_attr attr, value
      config.attribute(attr.to_sym, Helpers.determine_type(value))
    end
def add_model_attr attr, value
      config.attribute(attr.to_sym, Helpers.determine_type(value))
    end
Dynamically add a Virtus attr, detect Boolean, Integer, and Float types
 based on the value, otherwise just treat it like a string.
 Modifies the config instance variable
 TODO: May also be able to detect arrays

 @param attr [#to_sym] the name for the attr, e.g. "json_array"
 @param value [String] the value of the attr, e.g. "yes"
 @return [undefined]
 @api private