Permissions issues with PrivateJsonFile on windows

[soxofaan]

Windows does not support fine grained linux style permission chmoding, causing perrmission issues like

File "D:\tmp\env\lib\site-packages\openeo\rest\auth\config.py", line 85, in _write
    assert_private_file(self._path)
  File "D:\tmp\env\lib\site-packages\openeo\rest\auth\config.py", line 30, in assert_private_file
    p=path, a=mode, e=_PRIVATE_PERMS)
PermissionError: File C:\Users\john\AppData\Local\Temp\win-perms-test.json is readable by others: st_mode 100666 (expected permissions: 600).```

[soxofaan]

did a first quick fix to make OIDC at least usable on Windows:
now a warning is raised when permissions are not correctly set

[soxofaan]

next step: investigate oschmod (https://pypi.org/project/oschmod/) to set permissions on windows fully (which does not work with vanilla os.chmod)

[soxofaan]

Also interesting solution: some kind of logout feature to remove these local files: #250

[soxofaan]

FYI failing tests related to this are blocker for

• Provide openeo package on conda-forge #176