Port Bilanzierung to BO4E-python

[hf-kklein]

• Port our own (Hochfrequenz) Business Object Bilanzierung to Python.
• Add tests (to the python implementation) as usual
• Put focus on a well documented data model (docstrings) Ask for help if necessary.
• If the CI passes let someone from the Hochfrequenz team review it
• Do not merge it to bo4e/BO4E-Python yet! We want to use th BO Bilanzierung to establish a git based workflow to enhance the official BO4E standard (meaning: someone from another company with functional knowledge should review it)

fyi @hf-krechan

[DeltaDaniel]

bo4e/BO4E-python#508