More reliable and simpler canteen list handling

[COM8]

Fixes #282 by directly providing a --canteen-ids parameter that prints canteen id and exits.
That way we do not have to rely on the additional parser script that can handle only stdin input.

Fixes the following CI crash:

Traceback (most recent call last):
  File "/home/runner/work/eat-api/eat-api/scripts/parse_canteen_list.py", line 7, in <module>
    canteens = json.load(sys.stdin)
               ^^^^^^^^^^^^^^^^^^^^
  File "/opt/hostedtoolcache/Python/3.11.11/x64/lib/python3.11/json/__init__.py", line 293, in load
    return loads(fp.read(),
           ^^^^^^^^^^^^^^^^
  File "/opt/hostedtoolcache/Python/3.11.11/x64/lib/python3.11/json/__init__.py", line 346, in loads
    return _default_decoder.decode(s)
           ^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/hostedtoolcache/Python/3.11.11/x64/lib/python3.11/json/decoder.py", line 337, in decode
    obj, end = self.raw_decode(s, idx=_w(s, 0).end())
               ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^
  File "/opt/hostedtoolcache/Python/3.11.11/x64/lib/python3.11/json/decoder.py", line 355, in raw_decode
    raise JSONDecodeError("Expecting value", s, err.value) from None
json.decoder.JSONDecodeError: Expecting value: line 1 column 1 (char 0)

https://github.com/TUM-Dev/eat-api/actions/runs/13218416986/job/36900479138

[Friendly-Banana]

LGTM