Issue #387 openeo.connect, reinstate old behavior: no PermissionError on Windows

[JohanKJSchreurs]

Issue #387 Quick fix, reinstate old behavior: no PermissionError on Windows for PrivateJsonFile, log message instead

Fixes #387

Reinstated the old behavior of authenticate_oidc on Windows:
When PrivateJsonFile may be readable by others, log message instead of raising a PermissionError.

There is a follow-up issue here #400, if we still want to find a more secure solution for Windows.
To be decided.

Also, for now I have left in the code that uses oschmod because:

1. when it does work, then it still adds a bit more security;
2. we would like to get a solution out quickly, but removing oschmod cleanly takes a bit more work and care.