Add CTU data example and parser

[cchwala]

To get the CZ Tmobile data stream in, we also need a parser. Specifically we need:

TODO CTU:

• Example JSON data and metadata in a new dir in https://github.com/OpenSenseAction/GMDI_prototype/blob/main/parser/parsers
• A parser for this data and metadata in the same dir (probably needs to return a pd.DataFrame conforming to what is done in https://github.com/OpenSenseAction/GMDI_prototype/blob/main/parser/validate_dataframe.py, but not sure...)
• connect parser to db_writer.py (maybe needs multi-user system first and then do this via config file)
• A simple test (if possible 😉)

TODO @cchwala:

• allow forwarding of SFTP request
• create user for CTU
• later extend to multi-user system also for frontend