This merge request adds the customizing pattern from the json serialization to the xml serialization - which is now not necessary anymore for it's original usecase, but will be useful for parsing stripped xml elements in the http api.
Furthermore, the functions
read_aas_xml_element() were added.
read_aas_xml_element() should originally accept a type and a decoder class, but because mypy doesn't narrow down type variables for
if type_ is SomeType and the issue was still present with
if issubclass(type_, SomeType), despite it narrowing down the type, I decided to change the API and just pass a constructor function to it, as I think that it is prettier than telling mypy to ignore the type at the end of each line.